Is there a typo in #1. Should it be +63 and not –63?
Oops, sorry for the typo in the title. :|
Need help with these please:
In the expansion of (1-ax)^n, the first three terms are 1-12x-63x^2. Find the values of a and n.
and
In the expansion of (x-(1/x^2))^8 find:
a) The term that has x^-1
b) The coefficient of the term that has x^2.
Just to make the second one a little clearer, here's something I whipped up with my MSPaint skills:
rearrange (x-(1/x^2))^8, to:
(1/x^16) (1-x^3)^8 = (1/x^16)[1+8x^3+28x^6+54x^9+70x^12+54x^15+
...................28x^18+8x^21+x^24]
a) so the coefficient of x^(-1) in this is the coefficient of x^15 in the []'s,
so is 54.
b) so the coefficient of x^2 in this is the coefficient of x^18 in the []'s,
so is 28.
RonL