P. S. It has ONLY 3 roots, since 3 the highest power of x. One "real" and two "complex". It is highly involved and was generated by computer.
Solve for x:
x^3+x^2 = 243
Subtract 243 from both sides:
x^3+x^2-243 = 0
Eliminate the quadratic term by substituting y = x+1/3:
-243+(y-1/3)^2+(y-1/3)^3 = 0
Expand out terms of the left hand side:
y^3-y/3-6559/27 = 0
If y = z+lambda/z then z = 1/2 (y+sqrt(y^2-4 lambda)) which will be used during back substitution:
-6559/27+1/3 (-z-lambda/z)+(z+lambda/z)^3 = 0
Multiply both sides by z^3 and collect in terms of z:
-(6559 z^3)/27+z^6+lambda^3+z^4 (3 lambda-1/3)+z^2 (3 lambda^2-lambda/3) = 0
Substitute lambda = 1/9 and then u = z^3, yielding a quadratic equation in the variable u:
u^2-(6559 u)/27+1/729 = 0
Find the positive solution to the quadratic equation:
u = 1/54 (6559+81 sqrt(6557))
Substitute back for u = z^3:
z^3 = 1/54 (6559+81 sqrt(6557))
Taking cube roots gives (6559+81 sqrt(6557))^(1/3)/(3 2^(1/3)) times the third roots of unity:
z = 1/3 (1/2 (6559+81 sqrt(6557)))^(1/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Substitute back for z = y/2+1/2 sqrt(y^2-(4)/9):
y/2+1/2 sqrt(y^2-(4)/9) = 1/3 (1/2 (6559+81 sqrt(6557)))^(1/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Rewrite the left hand side by combining fractions. y/2+1/2 sqrt(y^2-(4)/9) = 1/6 (3 y+sqrt(9 y^2-4)):
1/6 (3 y+sqrt(9 y^2-4)) = 1/3 (1/2 (6559+81 sqrt(6557)))^(1/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Multiply both sides by 6:
3 y+sqrt(9 y^2-4) = 2^(2/3) (6559+81 sqrt(6557))^(1/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 3 y from both sides:
sqrt(9 y^2-4) = 2^(2/3) (6559+81 sqrt(6557))^(1/3)-3 y or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Raise both sides to the power of two:
9 y^2-4 = (2^(2/3) (6559+81 sqrt(6557))^(1/3)-3 y)^2 or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Expand out terms of the right hand side:
9 y^2-4 = 9 y^2-6 2^(2/3) (6559+81 sqrt(6557))^(1/3) y+2 2^(1/3) (6559+81 sqrt(6557))^(2/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 9 y^2-6 2^(2/3) (6559+81 sqrt(6557))^(1/3) y+2 2^(1/3) (6559+81 sqrt(6557))^(2/3) from both sides:
6 2^(2/3) (6559+81 sqrt(6557))^(1/3) y-4-2 2^(1/3) (6559+81 sqrt(6557))^(2/3) = 0 or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Factor constant terms from the left hand side:
2 (3 2^(2/3) (6559+81 sqrt(6557))^(1/3) y-2-2^(1/3) (6559+81 sqrt(6557))^(2/3)) = 0 or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Divide both sides by 2:
3 2^(2/3) (6559+81 sqrt(6557))^(1/3) y-2-2^(1/3) (6559+81 sqrt(6557))^(2/3) = 0 or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Add 2+2^(1/3) (6559+81 sqrt(6557))^(2/3) to both sides:
3 2^(2/3) (6559+81 sqrt(6557))^(1/3) y = 2+2^(1/3) (6559+81 sqrt(6557))^(2/3) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Divide both sides by 3 2^(2/3) (6559+81 sqrt(6557))^(1/3):
y = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Substitute back for y = x+1/3:
x+1/3 = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 1/3 from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or z = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Substitute back for z = y/2+1/2 sqrt(y^2-(4)/9):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or y/2+1/2 sqrt(y^2-(4)/9) = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Rewrite the left hand side by combining fractions. y/2+1/2 sqrt(y^2-(4)/9) = 1/6 (3 y+sqrt(9 y^2-4)):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 1/6 (3 y+sqrt(9 y^2-4)) = -1/3 (1/2 (-6559-81 sqrt(6557)))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Multiply both sides by 6:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 3 y+sqrt(9 y^2-4) = -2^(2/3) (-6559-81 sqrt(6557))^(1/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 3 y from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or sqrt(9 y^2-4) = -2^(2/3) (-6559-81 sqrt(6557))^(1/3)-3 y or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Raise both sides to the power of two:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 9 y^2-4 = (-2^(2/3) (-6559-81 sqrt(6557))^(1/3)-3 y)^2 or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Expand out terms of the right hand side:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 9 y^2-4 = 9 y^2+6 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y+2 2^(1/3) (-6559-81 sqrt(6557))^(2/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 9 y^2+6 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y+2 2^(1/3) (-6559-81 sqrt(6557))^(2/3) from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or -6 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y-4-2 2^(1/3) (-6559-81 sqrt(6557))^(2/3) = 0 or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Factor constant terms from the left hand side:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or -2 (3 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y+2+2^(1/3) (-6559-81 sqrt(6557))^(2/3)) = 0 or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Divide both sides by -2:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 3 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y+2+2^(1/3) (-6559-81 sqrt(6557))^(2/3) = 0 or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 2+2^(1/3) (-6559-81 sqrt(6557))^(2/3) from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or 3 2^(2/3) (-6559-81 sqrt(6557))^(1/3) y = -2-2^(1/3) (-6559-81 sqrt(6557))^(2/3) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Divide both sides by 3 2^(2/3) (-6559-81 sqrt(6557))^(1/3):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or y = -((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Substitute back for y = x+1/3:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x+1/3 = -((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Subtract 1/3 from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or z = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Substitute back for z = y/2+1/2 sqrt(y^2-(4)/9):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or y/2+1/2 sqrt(y^2-(4)/9) = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Rewrite the left hand side by combining fractions. y/2+1/2 sqrt(y^2-(4)/9) = 1/6 (3 y+sqrt(9 y^2-4)):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 1/6 (3 y+sqrt(9 y^2-4)) = 1/3 (-1)^(2/3) (1/2 (6559+81 sqrt(6557)))^(1/3)
Multiply both sides by 6:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 3 y+sqrt(9 y^2-4) = (-2)^(2/3) (6559+81 sqrt(6557))^(1/3)
Subtract 3 y from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or sqrt(9 y^2-4) = (-2)^(2/3) (6559+81 sqrt(6557))^(1/3)-3 y
Raise both sides to the power of two:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 9 y^2-4 = ((-2)^(2/3) (6559+81 sqrt(6557))^(1/3)-3 y)^2
Expand out terms of the right hand side:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 9 y^2-4 = 9 y^2-6 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y-2 (-2)^(1/3) (6559+81 sqrt(6557))^(2/3)
Subtract 9 y^2-6 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y-2 (-2)^(1/3) (6559+81 sqrt(6557))^(2/3) from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 6 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y-4+2 (-2)^(1/3) (6559+81 sqrt(6557))^(2/3) = 0
Factor constant terms from the left hand side:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 2 (3 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y-2+(-2)^(1/3) (6559+81 sqrt(6557))^(2/3)) = 0
Divide both sides by 2:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 3 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y-2+(-2)^(1/3) (6559+81 sqrt(6557))^(2/3) = 0
Subtract (-2)^(1/3) (6559+81 sqrt(6557))^(2/3)-2 from both sides:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or 3 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3) y = 2-(-2)^(1/3) (6559+81 sqrt(6557))^(2/3)
Divide both sides by 3 (-2)^(2/3) (6559+81 sqrt(6557))^(1/3):
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or y = 1/3 (-1)^(2/3) ((6559+81 sqrt(6557))/(2))^(1/3)-1/3 ((-2)/(6559+81 sqrt(6557)))^(1/3)
Substitute back for y = x+1/3:
x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or x+1/3 = 1/3 (-1)^(2/3) ((6559+81 sqrt(6557))/(2))^(1/3)-1/3 ((-2)/(6559+81 sqrt(6557)))^(1/3)
Subtract 1/3 from both sides:
Answer: | x = (2+2^(1/3) (6559+81 sqrt(6557))^(2/3))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3))-1/3 or x = -1/3-((-1)^(2/3) (-2-2^(1/3) (-6559-81 sqrt(6557))^(2/3)))/(3 2^(2/3) (6559+81 sqrt(6557))^(1/3)) or x = 1/3 (-1)^(2/3) ((6559+81 sqrt(6557))/(2))^(1/3)+(-1/3-1/3 (-2/(6559+81 sqrt(6557)))^(1/3))