(3f-9)(5f+15)=0

Solution for (3f-9)(5f+15)=0 equation:

Simplifying
(3f + -9)(5f + 15) = 0

Reorder the terms:
(-9 + 3f)(5f + 15) = 0

Reorder the terms:
(-9 + 3f)(15 + 5f) = 0

Multiply (-9 + 3f) * (15 + 5f)
(-9(15 + 5f) + 3f * (15 + 5f)) = 0
((15 * -9 + 5f * -9) + 3f * (15 + 5f)) = 0
((-135 + -45f) + 3f * (15 + 5f)) = 0
(-135 + -45f + (15 * 3f + 5f * 3f)) = 0
(-135 + -45f + (45f + 15f2)) = 0

Combine like terms: -45f + 45f = 0
(-135 + 0 + 15f2) = 0
(-135 + 15f2) = 0

Solving
-135 + 15f2 = 0

Solving for variable 'f'.

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

Add '135' to each side of the equation.
-135 + 135 + 15f2 = 0 + 135

Combine like terms: -135 + 135 = 0
0 + 15f2 = 0 + 135
15f2 = 0 + 135

Combine like terms: 0 + 135 = 135
15f2 = 135

Divide each side by '15'.
f2 = 9

Simplifying
f2 = 9

Take the square root of each side:
f = {-3, 3}