Resposta :
Oi!
a) x(x-9)=0
X= 0 / X-9=0
X=0 / X= 9
b) x^2-81=0
X^2=81
X=+/-9
X^2-64=0
X^2=64
X=+/-8
X^2+20x=0
X(x+20)=0
X=0/ x=-20
X^2-x=0
X(x-1)=0
X=0 / x=1.
a) x(x-9)=0
X= 0 / X-9=0
X=0 / X= 9
b) x^2-81=0
X^2=81
X=+/-9
X^2-64=0
X^2=64
X=+/-8
X^2+20x=0
X(x+20)=0
X=0/ x=-20
X^2-x=0
X(x-1)=0
X=0 / x=1.