Ex 8.2,5 - Chapter 8 Class 11 Binomial Theorem

Transcript

Ex 8.2,5 Find the 4th term in the expansion of (x 2y)12 . We know that General term of expansion (a + b)n is Tr+1 = nCr an r br We need to find fourth term i.e. T4 = T3+1 of expansion (x 12y)12 Putting r = 3 , a = x , b = 2y , n = 12 T3+1 = 12C3 (x)12 3 ( 2y)3 = 12 ! 3! (12 3) ! x9 ( 2)3 (y)3 = 12! 3! 9! x9 ( 8) y3 = 12 11 10 9! 3 2 9 ! ( 8) x9 y3 = 12 11 10 ( 8) 6 x9 y3 = 2 11 10 ( 8) x9 y3 = 220 8 x9 y3 = 1760 x9 y3