f(x)=(x-3)(x+1)

Solution for f(x)=(x-3)(x+1) equation:

Simplifying
f(x) = (x + -3)(x + 1)

Multiply f * x
fx = (x + -3)(x + 1)

Reorder the terms:
fx = (-3 + x)(x + 1)

Reorder the terms:
fx = (-3 + x)(1 + x)

Multiply (-3 + x) * (1 + x)
fx = (-3(1 + x) + x(1 + x))
fx = ((1 * -3 + x * -3) + x(1 + x))
fx = ((-3 + -3x) + x(1 + x))
fx = (-3 + -3x + (1 * x + x * x))
fx = (-3 + -3x + (1x + x2))

Combine like terms: -3x + 1x = -2x
fx = (-3 + -2x + x2)

Solving
fx = -3 + -2x + x2

Solving for variable 'f'.

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

Divide each side by 'x'.
f = -3x-1 + -2 + x

Simplifying
f = -3x-1 + -2 + x

Reorder the terms:
f = -2 + -3x-1 + x