Question

Hyung-eun is solving the quadratic equation x2−4x−12=0
by grouping. Her work is shown below. At which step does Hyung-eun first make an error?

x2−4x−12=0


x(x−6)+2(x−6)=0


Step1: x2+(−6x)+2x−12=0

Step 2: (x2+(−6x))+(2x−12)=0

Step 3: x(x+(−6))+2(x−6)=0

Step 4: (x+6)(x−2)=0

Step 5: x+6=0
or x−2=0

x=−6
or x=2


(1 point)

Step 3

Step 1

Step 4

Step 2

Answer 1

Step 4.

When factoring out (x−6) from x(x−6)+2(x−6) you get (x+2)(x−6) (or (x−6)(x+2)), not (x+6)(x−2).