f(1)=7×1-8
f(1)=7-8
f(1)=-1
f(2)=7×2-8
f(2)=14-8
f(2)=6
f(7)=7×7-8
f(7)=49-8
f(7)=41
f(9)=7×9-8
f(9)=63-8
f(9)=55
f(0)=7×0-8
f(0)=-8
f(-1)=7×(-1)-8
f(-1)=-7-8
f(-1)=-15
f(-3)=7×(-3)-8
f(-3)=-21-8
f(-3)=-29
f(1/7)=7×1/7-8
f(1/7)=1-8
f(1/7)=-7
f(3/2)=7×3/2-8
f(3/2)=21/2-8
f(3/2)=21-16
f(3/2)=5