f(x)=(x-1)(x-7)(x+2)
Roots are derived from setting the three binomials equal to zero, thus x should be opposite of the term being subtracted or added. For example, in (x-1), we know that x=1 will cause the binomial to equal zero because 1-1=0. The same applies for (x-7) and (x+2), where x must set the equation equal to zero. So, x=7 and x=-2 would set the equations equal to 0.