find the first three terms in the expansion of (r-2s)power of 8

Answer 1

(r - 2s)^8
= r^8 + C(8,1)(r^7)(-2s) + C(8,2)(r^6)(-2s)^2 + ....
= r^8 - 16sr^7 + 112(s^2)(r^6) + ....