x^2-8x=20
Move +20 to the other side. Sign changes from +20 to -20
x^2-8x-20=20-20
x^2-8x-20=0
Think about two numbers that equals to -20 and -8.
(x-10)(x+2)=0
x-10=0 ( move -10 to the other side). Sign changes from -10 to 10
x-10+10=0+10
x=10
x+2=0 ( move +2 to the other side). Sign changes from +2 to -2
x+2-2=0-2
x=-2
Answer:
x=10, x=-2
