Question

Find the coefficient of x^5y^7 in the expansion of (5x+2y)^12

12 (x)^5 (2y)^7
3
My answer which i got wrong is 220x^5(128y^7)= 28160x^5y^7

Answer 1

12C5 (5x)^5 (2y)^7

12C5 * 5^5 * 2^7

792 * 3125 * 128 = 316800000

Answer 2

Where did 792 come from ? Also, thank you for helping me

Answer 3

huh? You surely must see from Scott's lines of text that

792 = 12C5