#1**0 **

Solve for r:

1/(r^3 + 7) - 7 = -r^3/(r^3 + 7)

Multiply both sides by r^3 + 7:

1 - 7 (r^3 + 7) = -r^3

Expand out terms of the left hand side:

-7 r^3 - 48 = -r^3

Add r^3 + 48 to both sides:

-6 r^3 = 48

Divide both sides by -6:

r^3 = -8

Taking cube roots gives 2 (-1)^(1/3) times the third roots of unity:

**r = -2 or r = 2 (-1)^(1/3) or r = -2 (-1)^(2/3)**

Guest Sep 22, 2019