WAEC Mathematics Past Questions & Answers - Page 128

636.

If y = \(\frac{(2\sqrt{x^2 + m})}{3N}\), make x the subject of the formular

A.

\(\frac{\sqrt{9y^2 N^2 - 2m}}{3}\)

B.

\(\frac{\sqrt{9y^2 N^2 - 4m}}{2}\)

C.

\(\frac{\sqrt{9y^2 N^2 - 3m}}{2}\)

D.

\(\frac{\sqrt{9y^2 N - 3m}}{2}\)

Correct answer is B

y = \(\frac{(2\sqrt{x^2 + m})}{3N}\)

3yN = 2(\(\sqrt{x^2 + m})\)

\(\frac{3yN}{2} = \sqrt{x^2 + m}\)

(\(\frac{3yN}{2})^2 = ( \sqrt{x^2 + m})\)

\(\sqrt{\frac{9y^2N^2}{4} - \frac{m}{1}}\)

x = \(\frac{\sqrt{9Y^2N^2 - 4m}}{4}\)

x = \(\frac{\sqrt{9y^2N^2 - 4m}}{2}\)

637.

The sum of the exterior of an n-sided convex polygon is half the sum of its interior angle. find n

A.

6

B.

8

C.

9

D.

12

Correct answer is A

sum of exterior angles = 360o

Sum of interior angle = (n - 2) x 180

360 = \(\frac{1}{2}\) x(n - 2) x 180(90o)

360 = \(\frac{1}{2}\) x(n - 2) x 90o

\(\frac{360}{90}\) = a - 2

4 = n - 2

n = 4 + 2 = 6

638.

Simplify \(\frac{2}{2 + x} + \frac{2}{2 - x}\)

A.

\(\frac{4}{4 - x^3}\)

B.

\(\frac{8}{4 - x^2}\)

C.

\(\frac{4x}{4 - x^2}\)

D.

\(\frac{8 - 4x}{4 - x^2}\)

Correct answer is B

\(\frac{2}{2 + x} + \frac{2}{2 - x}\)

\(\frac{2(2 - x) + 2(2 + x)}{(2 + x)(2 - x)} = \frac{4 - 2x + 4 + 2x}{4 - 2x + 2x - x^2}\)

= \(\frac{8}{4 - x^2}\)

639.

What is the length of a rectangular garden whose perimeter is 32cm and area 39cm2?

A.

25cm

B.

18cm

C.

13cm

D.

9cm

Correct answer is C

perimeter = 2(l + b) = 32

l + b = \(\frac{32}{2}\)

l + b = 16

b = 16 - 1.......(1)

Area = l + b = 39

lb = 39 .....(2)

put (1) into (2)

l(16 - 1) = 39

16l - l2 = 39

l2 = 13l - 3l + 39 = 0

l(l - 13) - 3(1 - 13) = 0

(l - 3)(l + 130 = 0

l - 3 = 0 or l - 13 = 0

l = 3cm or l = 13cm; The length in 13cm

640.

Given that tan x = 1, where 0o \(\geq\) x 90o, evaluate \(\frac{1 - \sin^2 x}{\cos x}\)

A.

2\(\sqrt{2}\)

B.

\(\sqrt{2}\)

C.

\(\frac{\sqrt{2}}{2}\)

D.

\(\frac{1}{2}\)

Correct answer is C

Given tan x = 1

x = tan-1(1)

x = 45o

Now, \(\frac{1 - ( \frac{1}{\sqrt{2} )^2}}{\frac{1}{\sqrt{2}}}\)

= \(\frac{1 - \frac{1}{2}}{\frac{1}{2}}\)

= \(\frac{1}{2} + \frac{1}{\sqrt{2}}\)

= \(\frac{1}{2} \times \frac{1}{\sqrt{2}}\)

= \(\frac{\sqrt{2}}{2}\)