suppose x+1/x =3. evaluate x^3 + 1/x^3
I started by cubed both sides and now im lost. please help
x^3 + 1/x^3 = 21.
1) Start with the equation x + 1/x = 3
Multiply both sides by x, giving you a quadratic.
Solve this quadratic (use the quadratic formula).
2) Take each of the two answers from part 1) and place them into the expression: x3 + 1/x3
(x + 1/x)3 = x3 + 3(x2)(1/x) + 3(x)(1/x2) + 1/x3 = x3 + 3x + 3/x + 1/x3
x3 + 1/x3 = (x + 1/x)3 - 3(x + 1/x) = 33 - 3(3) = 27 - 9 = 18.
