Find the root of (x-1)(x-4)=0

Question

find all roots

Answer 1

The roots are the values of x for which (x-1)(x+4) equals zero.  That will occur when either factor, (x-1) or (x+4), equals zero.  (x-1 ) equals zero when x = 1, so that's one of the roots.  I'll leave it to you to find the other (hint: what value of x makes (x+4)=0?)