.66x^2+3.92-9=15

Solution for .66x^2+3.92-9=15 equation:

Simplifying
0.66x2 + 3.92 + -9 = 15

Reorder the terms:
3.92 + -9 + 0.66x2 = 15

Combine like terms: 3.92 + -9 = -5.08
-5.08 + 0.66x2 = 15

Solving
-5.08 + 0.66x2 = 15

Solving for variable 'x'.

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

Add '5.08' to each side of the equation.
-5.08 + 5.08 + 0.66x2 = 15 + 5.08

Combine like terms: -5.08 + 5.08 = 0.00
0.00 + 0.66x2 = 15 + 5.08
0.66x2 = 15 + 5.08

Combine like terms: 15 + 5.08 = 20.08
0.66x2 = 20.08

Divide each side by '0.66'.
x2 = 30.42424242

Simplifying
x2 = 30.42424242

Take the square root of each side:
x = {-5.515817475, 5.515817475}