WAEC Further Mathematics Past Questions & Answers - Page 72

356.

Given \(\sin \theta =  \frac{\sqrt{3}}{2}, 0° \leq \theta \leq 90°\), find \(\tan 2\theta\) in surd form

A.

\(- \sqrt{3}\)

B.

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

C.

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

D.

\(\sqrt{3}\)

Correct answer is A

\(\sin \theta = \frac{\sqrt{3}}{2} \implies opp = \sqrt{3}; hyp = 2\)

\(adj^{2} = 2^{2} - (\sqrt{3})^{2} = 1 \implies adj = 1\)

\(\cos \theta = \frac{1}{2}\)

\(\sin 2\theta = \sin (180 - \theta) = \sin \theta = \frac{\sqrt{3}}{2}\)

\(\cos 2\theta = \cos (180 - \theta) = -\cos \theta = -\frac{1}{2}\)

\(\tan 2\theta = \frac{\sin 2\theta}{\cos 2\theta} = \frac{\frac{\sqrt{3}}{2}}{-\frac{1}{2}}\)

= \(- \sqrt{3}\)

357.

The coordinates of the centre of a circle is (-2, 3). If its area is \(25\pi cm^{2}\), find its equation. 

A.

\(x^{2} + y^{2} - 4x - 6y - 12 = 0\)

B.

\(x^{2} + y^{2} - 4x + 6y - 12 = 0\)

C.

\(x^{2} + y^{2} + 4x + 6y - 12 = 0\)

D.

\(x^{2} + y^{2} + 4x - 6y - 12 = 0\)

Correct answer is D

Equation of a circle with centre coordinates (a, b) : \((x - a)^{2} + (y - b)^{2} = r^{2}\)

Area of circle = \(\pi r^{2} = 25\pi cm^{2} \implies r^{2} = 25 \)

\(\therefore r = 5cm\)

(a, b) = (-2, 3)

Equation: \((x - (-2))^{2} + (y - 3)^{2} = 5^{2}\)

\(x^{2} + 4x + 4 + y^{2} - 6y + 9 = 25 \implies x^{2} + y^{2} + 4x - 6y + 13 - 25 = 0\)

= \(x^{2} + y^{2} + 4x - 6y - 12 = 0\)

358.

The line \(y = mx - 3\) is a tangent to the curve \(y = 1 - 3x + 2x^{3}\) at (1, 0). Find the value of the constant m.

A.

-4

B.

-1

C.

3

D.

4

Correct answer is C

\(y = 1 - 3x + 2x^{3}\)

\(\frac{\mathrm d y}{\mathrm d x} = -3 + 6x^{2}\)

At (1, 0), \(\frac{\mathrm d y}{\mathrm d x} = -3 + 6(1^{2}) = -3 + 6 = 3\)

\(y = mx - 3 \implies \frac{\mathrm d y}{\mathrm d x} = m = 3\) (Tangent with equal gradient)

359.

If (x + 3) is a factor of the polynomial \(x^{3} + 3x^{2} + nx - 12\), where n is a constant, find the value of n.

A.

-1

B.

-2

C.

-3

D.

-4

Correct answer is D

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

Using remainder theorem, if x + 3 is a factor, f(-3) = 0.

\(f(-3) = (-3)^{3} + 3(-3)^{2} + n(-3) - 12 = 0\)

\(-27 + 27 - 3n - 12 = 0 \implies -3n = 12\)

\(n = -4\)

360.

Solve \(x^{2} - 2x - 8 > 0\).

A.

x < -4 or x > 2

B.

x < -2 or x > 4

C.

-2 < x < 4

D.

-4 < x < 2

Correct answer is B

No explanation has been provided for this answer.