I was working on a problem with an affine cipher. Looking at the properties they say for "f(x)=(ax + b)MOD26 defines a valid affine cipher if a is relatively prime to 26, and b is an integer between 0 and 25."

i was working with f(x)=-9x+12(mod26),so K=A, H=B... but f(x)=11x-170(mod26) gives the same answers but 170 isn't between 0 and 25?

Can someone explain this?