JAMB Mathematics 1978 Question 3

Question 3

Algebraic Expressions

Multiply (x + 3y + 5) by (2x² + 5y + 2)

A.2x³+3yx²+10xy+15y²+13y+10x²+2x+10
B.2x³+6yx²+5xy+15y²+31y+10x²+2x+10
C.2x³+3yx²+5xy+10y²+13y+5x²+2x+10
D.2x³+6yx²+5xy+15y²+13y+10x²+2x+10
E.2x³+2yx²+10xy+10y²+31y+5x²+2x+10

Show the answer and explanation

Answer: B (2x³+6yx²+5xy+15y²+31y+10x²+2x+10)

Explanation

Multiply each term of the first bracket by each term of the second: x gives 2x³ + 5xy + 2x, 3y gives 6x²y + 15y² + 6y, and 5 gives 10x² + 25y + 10. Collecting the y terms gives 31y.