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WAEC Mathematics Past Questions & Answers - Page 82

406.

Adding 42 to a given positive number gives the same result as squaring the number. Find the number

Correct answer is C

Let the given positive number be x

Then 4 + x = x²

0 = x² - x - 42

or x² - x - 42 = 0

x² - 7x + 6x - 42 = 0

x(x - 7) + 6(x - 7) = 0

= (x + 6)(x - 7) = 0

x = -6 or x = 7

Hence, x = 7

407.

If m = 4, n = 9 and r = 16., evaluate $\frac{m}{n}$ - 1 $\frac{7}{9}$ + $\frac{n}{r}$

1 $\frac{5}{16}$

1 $\frac{1}{16}$

$\frac{5}{16}$

- 1 $\frac{37}{48}$

View answer & explanation

Correct answer is D

If m = 4, n = 9, r = 16,

then $\frac{m}{n}$ - 1 $\frac{7}{9}$ + $\frac{n}{r}$

= $\frac{4}{9}$ - $\frac{16}{9}$ + $\frac{9}{16}$

= $\frac{64 - 256 + 81}{144}$

= $\frac{-111}{144}$

= - 1 $\frac{37}{48}$

408.

Find the equation whose roots are $\frac{3}{4}$ and -4

4x² - 13x + 12 = 0

4x² - 13x - 12 = 0

4x² + 13x - 12 = 0

4x² + 13x + 12 = 0

View answer & explanation

Correct answer is C

Let x = $\frac{3}{4}$ or x = -4

i.e. 4x = 3 or x = -4

(4x - 3)(x + 4) = 0

therefore, 4x² + 13x - 12 = 0

409.

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

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

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

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

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

View answer & explanation

Correct answer is B

6ax - 12by - 9ay + 8bx

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

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

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

410.

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

4y $^\frac{1}{3}$

4y $^-3$

2y $^\frac{1}{3}$

2y $^-3$

View answer & explanation

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 $^\frac{1}{3}$