Question

What is the coefficient of the third term in the binomial expansion of (a + b)6? 1 15 20 90

Answer 1

Answer:  15

Step-by-step explanation:

(r+1)th term of $(a+b)^n$ is given by:-

$T_{r+1}=\ ^nC_r(a)^{n-r}b^r$

For $(a+b)^6$ , n= 6

$T_3=T_{2+1}=\ ^6C_2(a)^{6-2}(b)^2$

$=\ \dfrac{6!}{4!2!}a^4b^2\ \ \ [^nC_r=\dfrac{n!}{r!(n-r)!}]\\\\=\dfrac{6\times5\times4!}{4!\times2}a^4b^2\\\\=3\times5a^4b^2\\\\ =15a^4b^2$

Hence, the coefficient of the third term in the binomial expansion of  $(a+b)^6$ is 15.

Answer 2

Answer:

15

Step-by-step explanation: