Question

if for positive integer r>1,n>2 the coefficients of the (3r)th and (r+2)th power of x in the expression of (1+x)^2n are equal then
A)2r=n
B) n=3r
C)n=2r+1
D)n=2r-1

Answer 1

i got it A pls anyone can check @ShadowLegendX @Directrix @ganeshie8 @Kainui

Answer 2

Can you expand the expression and write the general term?

Answer 3

2nC3r-1=2nCr+1

Answer 4

3r-1=2n-r-1

Answer 5

Or, 3r - 1 = r + 1 is also possible... but that would mean r = 1 which is not true...

Answer 6

Great after that ?

Answer 7

n=2r

Answer 8

is it right

Answer 9

Yeps! Great job!