Question

binomial expansion!! I’ve managed to do part a and got 64+192kx+240k^2x^2+160k^3x^3 but I’m not sure how to do part b. please could someone explain?

Answer 1

Hi,

Explanation:

a)

`(2+kx)^6=2^6+6*2^5*kx+15*2^4*(kx)^2+20*2^3*(kx)^3+15*2^2*(kx)^4+6*2*(kx)^5+(kx)^6\\\\=64+192kx+240k^2x^2+160k^3x^3+60k^4x^4+12k^5x^5+k^6x^6\\`

b)

`20*8*k^3x^3=-20x^3\\\\k^3=-(1)/(8) \\\\k=-(1)/(2)`