If the constant term in the binomial expansion of x - k x 2 10 is 405 , then k equals :

Question

Aicharya · Accepted Answer

T r + 1 = C r 10 - k x 2 r x 10 - r = C r &#183; 10 - k r &#183; x 5 - 5 r 2 for constant term &#8658; 5 - 5 r 2 = 0 &#160; &#160; &#8658; r = 2 &#8658; T 3 = C 2 10 &#183; k 2 = 405 &#8658; 10 ( 9 ) 2 k 2 = 405 &#8658; k 2 = 9 &#8658; k = 3

If the constant term in the binomial expansion of x - k x 2 10 is 405 , then k equals :

Solution