Question 311704
Solve:
{{{(x-8)(x+1) = -20}}} First, multiply the two factors on the left side using the FOIL method.
{{{x^2+x-8x-8 = -20}}} Simplify the left side.
{{{x^2-7x-8 = -20}}} Now add 20 to both sides to get the equation in standard form:{{{ax^2+bx+c = 0}}}.
{{{x^2-7x-8+20 = 0}}} Simplify.
{{{x^2-7x+12 = 0}}} Now you can apply the quadratic formula: {{{x = (-b+-sqrt(b^2-4ac))/2a}}} and, in your equation, a = 1, b = -7, and c = 12, so make the appropriate substitutions:
{{{x = (-(-7)+-sqrt((-7)^2-4(1)(12)))/2(1)}}} Simplify.
{{{x = (7+-sqrt(49-48))/2}}}
{{{x = (7+-sqrt(1))/2}}}
{{{x = (7+1)/2}}} or {{{(7-1)/2}}}
{{{highlight(x = 4)}}} or {{{highlight(x = 3)}}}