271

a)
\left(x+3\right)\left(x-3\right)=x^2-3^2=x^2-9
x^2=9
x=3
b)
\left(x+7\right)\left(x-7\right)=x^2-7^2
x^2=49
x=7
c)
\left(x+1\right)\left(x-1\right)=x^2-1^2
x^2=1
x=1