How do you factor x ^ { 2} - 10x = - 11x210x=11?

1 Answer
Nov 9, 2017

x^2-10x+11=(x-5-sqrt(14))(x-5+sqrt(14))x210x+11=(x514)(x5+14)

Explanation:

First, add 1111 to both sides of the equation

x^2-10x+11=-11+11x210x+11=11+11

x^2-10x+11 = 0x210x+11=0

There are no nice integers which multiply together to make +11+11 and add together to make -1010. So factoring will involve using either the quadratic equation or completing the square.

Let's choose completing the square. Rewrite the above equation with spaces to prepare for the next step.

(x^2-10x+" ")+11 + " "=0(x210x+ )+11+ =0

Take the coefficient of xx, in this case -1010, divide it by 22 and square the final result.

((-10)/2)^2=25(102)2=25

In the spaces provided, first add 2525, then subtract it, as follows:

(x^2-10x+25)+11-25=0(x210x+25)+1125=0

This makes a perfect square inside the parenthesis

(x-5)^2+11-25=0(x5)2+1125=0

(x-5)^2-14=0(x5)214=0

(x-5)^2=14(x5)2=14

Take the square root of both sides

x-5=+-sqrt(14)x5=±14

x=5+-sqrt(14)x=5±14

This gives two results

x=5+sqrt(14)x=5+14 and x=5-sqrt(14)x=514

Solving both for zero gives your factors

x-5-sqrt(14)=0x514=0 and x-5+sqrt(14)=0x5+14=0

Thus, the original equation factors as follows:

x^2-10x+11=(x-5-sqrt(14))(x-5+sqrt(14))x210x+11=(x514)(x5+14)