Factor and check x^2 - 21x + 108 = 0

x^2 - 21x + 108 = 0

(x )(x ) ( -12)( -9)=0

(x-12) (x-9) = 0

Check:

(x-12) (x-9) = 0

(x)(X) (x)(-9) (-12)(x) (-12)(-9)=0

x^2 -9x -12x +108=0

x^2 -21x +108=0