WAEC Mathematics Past Questions & Answers - Page 83

411.

Factorize completely: 6ax - 12by - 9ay + 8bx

A.

(2a - 3b)(4x + 3y)

B.

(3a + 4b)(2x - 3y)

C.

(3a - 4b)(2x + 3y)

D.

(2a + 3b)(4x -3y)

Correct answer is B

6ax - 12by - 9ay + 8bx

= 6ax - 9ay + 8bx - 12by

= 3a(2x - 3y) + 4b(2x - 3y)

= (3a + 4b)(2x - 3y)

412.

If 2n = y, Find 2\(^{(2 + \frac{n}{3})}\)

A.

4y\(^\frac{1}{3}\)

B.

4y\(^-3\)

C.

2y\(^\frac{1}{3}\)

D.

2y\(^-3\)

Correct answer is A

If 2n = y,

then, 2\(^{(2 + \frac{n}{3})}\) = 22 x 2\(^\frac{n}{3}\)

= 4 x (2n)\(^{\frac{1}{3}}\)

But y = 2n, hence

2\(^{(2 + \frac{n}{3})}\) = 4 x y\(^{\frac{1}{3}}\)

= 4y\(^\frac{1}{3}\)

413.

Given that logx 64 = 3, evaluate x log\(_2\)8

A.

6

B.

9

C.

12

D.

24

Correct answer is C

If logx 64 = 3, then \(64 = x^3\)

\(4^3 = x^3\)

Since the indices are equal,

x = 4

Hence, x log\(_2\)8 

= 4(3.log\(_2\)2)

= where log\(_2\)2 = 1(1)

= 12 X 1 

= 12

414.

Factorize \( x^2 − 2x − 15 \)

A.

(x + 3)2

B.

(x + 5)(x − 3)

C.

(x − 5)2

D.

(x − 5)(x + 3)

Correct answer is D

x2 − 2x − 15

(x2 − 5x) + (3x − 15)

x(x − 5)+ 3(x − 5)

(x − 5)(x + 3)

415.

Given that A = {1, 5, 7} B = {3, 9, 12, 15} C = {2, 4, 6, 8} Find (A ∪ B) ∪ C

A.

{1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15}

B.

{1, 2, 3, 5, 6, 8, 12, 15}

C.

{2, 4, 5, 9, 12, 15}

D.

{1, 5, 6, 7, 8, 9, 12, 15}

Correct answer is A

{A ∪ B ∪ C}

{A ∪ B} = {1, 3, 5, 7, 9, 12, 15}

∪ C={2,4,6,8}

{A ∪ B} ∪ C = {1, 3, 5, 7, 9, 12, 15} ∪ {2, 4, 6, 8}

= {1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15}

{A ∪ B} ∪ C = {1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15}