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WAEC Mathematics Past Questions & Answers - Page 104

516.

If 9^{(2 - x)} = 3, find x

$\frac{3}{2}$

$\frac{5}{2}$

View answer & explanation

Correct answer is B

9(2 - x) = 3

3^{2(2 - x)} = 3

2(2 - x) = 1

4 - 2x = 1

-2x = 1 - 4

-2x = -3

x = $\frac{-3}{-2}$

x = $\frac{3}{2}$

517.

Multiply 2.7 x 10^-4 by 6.3 x 10⁶ and leave your answers in standard form

1.7 x 10³

1.70 x 10³

1.701 x 10³

17.01 x 10³

View answer & explanation

Correct answer is C

2.7 x 10^-4 x 6.3 x 10⁶

= 2.7 x 6.3 x 10^-4 x 10⁶

= 17.01 x 10^{-4 + 6}

= 17.01 x 10²

= 1.701 x 10¹ x 10²

= 1.701 x 10^{1 + 2}

= 1.701 x 10³

518.

The diagram is a polygon. Find the largest of its interior angles

300^o

100^o

120^o

150^o

View answer & explanation

Correct answer is D

Sum of interior angles = 360²

i.e 3x + 2x + 2x + x + 4x = 360^o

12x = 360

x = $\frac{360}{12}$

x = 30^o

x + c = 180

30^o + c = 180

c = 180 - 30

c = 150^o

519.

The graph is that of y = 2x² - 5x - 3. For what value of x will y be negative? For what value of x will y be negative?

- $\frac{1}{2} \leq x$ < 3

- $\frac{1}{2} < x \leq 3$

- $\frac{1}{2} < x < 3$

- $\frac{1}{2} \leq x \leq 3$

View answer & explanation

Correct answer is C

2x² - 5x - 3 = 0

2x² - 6x + x - 3 = 0

2x(x - 3) + 1(x - 3) = 0

(2x + 1)(x - 3) = 0

2x + 1 = 0

2x = -1

x = - $\frac{1}{2}$

x - 3 = 0

- $\frac{1}{2}$ < x < 3

520.

In the diagram, |SR| = |QR|. < SRP = 65^o and < RPQ = 48^o, find < PRQ

65^o

45^o

25^o

19^o

View answer & explanation

Correct answer is D

< RSQ = < RPQ = 48^o (angle in the same segment)

< SQR < RSQ (Base angle of an isosceles $\bigtriangleup$ )

< SQR = 480

< QRS + < RSQ + < RSQ = 180^o(sum of interior angles of a $\bigtriangleup$ )

i.e. < QRS + 48^o + 48^o = 180

< QRS = 180 - (48 + 48) = 180 - 96 = 84^o

but < PRQ + < PRS = < QRS

< PRQ = < QRS - < PRS - 84 - 65

= 19^o