-2(13-r^2)=

Solution for -2(13-r^2)= equation:

Simplifying
-2(13 + -1r2) = 0
(13 * -2 + -1r2 * -2) = 0
(-26 + 2r2) = 0

Solving
-26 + 2r2 = 0

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '26' to each side of the equation.
-26 + 26 + 2r2 = 0 + 26

Combine like terms: -26 + 26 = 0
0 + 2r2 = 0 + 26
2r2 = 0 + 26

Combine like terms: 0 + 26 = 26
2r2 = 26

Divide each side by '2'.
r2 = 13

Simplifying
r2 = 13

Take the square root of each side:
r = {-3.605551275, 3.605551275}