higher maths

ted9308

Could anyone help me with this question just cant seem to get it out right-binomial theorem by the way "if h is a constant and hx(to the power of 4)y(squared) is a term of the expansion of (3x -4ysquared)to the power of n..find the value of n and h

straight_As

Post up what you've done so far and boards might be able to point you in the right direction.

It's pointless someone just posting up a solution though.

Term with: hx^4y^2 of BE: (3x-4y^2)^n

General term: Ur+1= nCr (3x)^n-r (-4y^2)^r

=nCr 3^n-r . x^n-r. (-4)^r. y^2r
= nCr (3^n-r. [-4]^r) x^n-r. y^2r

Power of x has to =4, and power of y has to =2
n-r=4
2r=2 r=1
n-1=4
n=5

U1+1= 5C1 (3^5-1. -4^1) x^5-1 y^2r
U2= 5C1 (3^4.-4) x^4 y^2

h= coefficient of term= 5C1 (81.-4) = 5 . -324 = -1620

U2= -1620x^4y^2

n=5, h= -1620




I think this is right, do you have the answer to check it with? Sorry if this is hard to follow! (^ means to the power of btw)