X

Shifting -20 to the other side:

X

Factorizing:

X

Taking common:

x(x-5)-4(x-5)=0

So:

(x-5)(x-4)=0

Hence:

x-5=0 or x-4=0

x=5 or x=4

^{2}-9x=-20Shifting -20 to the other side:

X

^{2}-9x+20=0Factorizing:

X

^{2}-5x-4x+20=0Taking common:

x(x-5)-4(x-5)=0

So:

(x-5)(x-4)=0

Hence:

x-5=0 or x-4=0

x=5 or x=4