finding zeros or setting y ot f(n) equal to zero
and all you have to do is factor it, hoping you know how to do this
5. 0= n^2-2n-15
(n-5)(n+3)= 0
n-5= 0 n+3=0
n=5 and n=-3
6.t^2+6t=27
t^2+6t-27=0
(t + 9) (t-3)= 0
t=-9 and t=3
7. x^2-9x=-18
x^2-9x+18=0
(x-6)(x-3)= 0
x=6 and x=3
8. a^2 - 7a = 30
a^2 - 7a -30= 0
(a-10)(a+3)=0
a=10 and a=-3
hope that helps