f(x)=(x+3)(x-1)
f(x)=0
(x+3)=0 (x-1)=0
x=-3. x=1
f(2)=(2+3)(2-1)
f(1/x)=(1/x-1) :(3-1/x)=(1-x)/x :(3x-1)x=(1-x)/x*x/((3x-1)=(1-x)/(3x-1)
f(x)=(x+3)(x-1)
f(x)=0
(x+3)=0 (x-1)=0
x=-3. x=1
f(2)=(2+3)(2-1)
f(1/x)=(1/x-1) :(3-1/x)=(1-x)/x :(3x-1)x=(1-x)/x*x/((3x-1)=(1-x)/(3x-1)