WAEC Further Mathematics Past Questions & Answers - Page 80

396.

If \(16^{3x} = \frac{1}{4}(32^{x - 1})\), find the value of x.

A.

\(-1\)

B.

\(\frac{-1}{3}\)

C.

\(\frac{-3}{7}\)

D.

\(\frac{-5}{19}\)

Correct answer is A

\(16^{3x} = \frac{1}{4}(32^{x - 1})\)

\((2^{4})^{3x} = (2^{-2})((2^{5})^{x - 1})\)

\(2^{12x} = 2^{-2 + 5x - 5}\)

\(12x = -7 + 5x\)

\(7x = -7 \implies x = -1\)

397.

If \(\frac{5}{\sqrt{2}} - \frac{\sqrt{8}}{8} = m\sqrt{2}\), where m is a constant. Find m.

A.

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

B.

\(1\frac{1}{4}\)

C.

\(2\frac{1}{4}\)

D.

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

Correct answer is C

\(\frac{5}{\sqrt{2}} = \frac{5 \times \sqrt{2}}{\sqrt{2} \times \sqrt{2}} = \frac{5\sqrt{2}}{2}\)

\(\frac{\sqrt{8}}{8} = \frac{2\sqrt{2}}{8} = \frac{\sqrt{2}}{4}\)

\(\frac{5}{\sqrt{2}} - \frac{\sqrt{8}}{8} = (\frac{5}{2} - \frac{1}{4})\sqrt{2}\)

= \(\frac{9}{4}\sqrt{2} \)

= \(2\frac{1}{4}\sqrt{2}\)

398.

Find the value of \(\cos(60° + 45°)\) leaving your answer in surd form

A.

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

B.

\(\frac{3 + \sqrt{6}}{4}\)

C.

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

D.

\(\frac{3 - \sqrt{6}}{4}\)

Correct answer is C

\(\cos (x + y) = \cos x \cos y - \sin x \sin y \)

\(\cos (60 + 45) = \cos 60 \cos 45 - \sin 60 \sin 45\)

= \(\frac{1}{2} \times \frac{\sqrt{2}}{2} - \frac{\sqrt{3}}{2} \times \frac{\sqrt{2}}{2}\)

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

399.

Find the domain of \(f(x) = \frac{x}{3 - x}, x \in R\), the set of real numbers.

A.

\({x : x \in R, x \neq 3}\)

B.

\({x : x \in R, x \neq 1}\)

C.

\({x : x \in R, x \neq 0}\)

D.

\({x : x \in R, x\neq -3}\)

Correct answer is A

\(f(x) = \frac{x}{3 - x} \)

f(x) has a defined value except at x = 3 where the function is undefined.

400.

Find, correct to two decimal places, the acute angle between \(p = \begin{pmatrix} 13 \\ 14 \end{pmatrix}\) and \(q = \begin{pmatrix} 12 \\ 5 \end{pmatrix}\).

A.

23.52°

B.

24.50°

C.

29.52°

D.

29.82°

Correct answer is B

\(p . q = |p||q|\cos \theta\)

\(156 + 70 = (\sqrt{13^{2} + 14^{2}})(\sqrt{12^{2} + 5^{2}}) \cos \theta\)

\(226 = (\sqrt{365})(13) \cos \theta\)

\(\frac{226}{13\sqrt{365}} = \cos \theta\)

\(\cos \theta = 0.9099\)

\(\theta = 24.50°\)