WAEC Mathematics Past Questions & Answers - Page 192

956.

A right circular cone is such that its radius r is twice its height h. Find its volume in terms of h

A.

\(\frac{2}{3}\pi h^2\)

B.

\(\frac{1}{12}\pi h^3\)

C.

\(\frac{4}{3}\pi h^2\)

D.

\(\frac{4}{3}\pi h^3\)

Correct answer is D

Volume of a cone = \(\frac{\pi r^2 h}{3}\)

r = 2h.

V = \(\frac{\pi \times (2h)^2 \times h}{3}\)

= \(\frac{4}{3} \pi h^3\)

957.

In the diagram /PS/ = 9 cm, /OR/ = 5cm, \(P\hat{S}R = 63^o\) and \(S\hat{P}Q = P\hat{Q}R = 90^o\). Find, correct to the nearest whole number, the area of the trapezium,

A.

55cm2

B.

25cm2

C.

22cm2

D.

13cm2

Correct answer is A

Considering the triangle in the diagram
\(tan\theta = \frac{opp}{hyp}\\
Tan 63^{\circ} = \frac{h}{4}\\
h = 4 tan 63^{\circ}\\
Area of trapezium = \frac{1}{2}h(a+b)\\
\left(\frac{1}{2} \times 4 tan 63^{\circ}[5+9]\right)\\
=28\times 1.963 = 54.96 = 55cm^2\)

959.

Evaluate Cos 45o Cos 30o - Sin 45o Sin 30o leaving the answer in surd form

A.

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

B.

\(\frac{\sqrt{3}-\sqrt{2}}{4}\)

C.

\(\frac{\sqrt{6}-\sqrt{2}}{2}\)

D.

\(\frac{\sqrt{6}-\sqrt{2}}{4}\)

Correct answer is D

\(cos45^o \times cos30^o - sin45^o \times sin30^o\\
\frac{1}{\sqrt{2}}\times \frac{\sqrt{3}}{2} - \frac{1}{\sqrt{2}}\times \frac{1}{2}\\
\frac{\sqrt{3}}{2\sqrt{2}}-\frac{1}{2\sqrt{2}}; = \frac{\sqrt{3}-1}{2\sqrt{2}}=\frac{\sqrt{6}-\sqrt{2}}{4}\)

960.

Find the equation whose roots are \(-\frac{2}{3}\) and 3

A.

3x2+11x-6=0

B.

3x2+7x+6=0

C.

3x2-11x-6=0

D.

3x2-7x-6=0

Correct answer is D

\(x = -\frac{2}{3} \implies x + \frac{2}{3} = 0\)

\(x = 3 \implies x - 3 = 0\)

\(\implies (x - 3)(x + \frac{2}{3}) = 0\)

\(x^2 - 3x + \frac{2}{3}x - 2 = 0\)

\(x^2 - \frac{7}{3}x - 2 = 0\)

\(3x^2 - 7x - 6 = 0\)