Question

Find the coefficient of x^3Y^2z^2 in (x+y+z)^7

Answer 1

( a + b + c) ^ n = Ó n ! / ( i! j! k! ) a ^ i b ^ j c ^ k

where i + j + k = n

So exponent of x ^ 3 y ^ 2 z ^ 2 =

7! / (3! 2! 2!) =

5040 / ( 6 * 2 * 2 ) =

5040 / 24 =

210

Answer 2

Ó mean summ