The coefficient of x3y in ( x + 2y) × (5x + y)3 is :
Answer & explanation
Correct answer: option 4
Given = (x + 2y) × (5x + y)3
= (x + 2y) × (5x + y)3
= (x + 2y) × (125x3 + y3 + 75x2y + 15xy2)
= 125x4 + xy3 + 75x3y + 15x2y2 + 250x3y + 2y4 + 150x2y2 + 30xy3
Coefficient of x3y = 75 + 250 = 325