WAEC Further Mathematics Past Questions & Answers - Page 102

506.

Given that \(P = \begin{pmatrix} y - 2 & y - 1 \\ y - 4 & y + 2 \end{pmatrix}\) and |P| = -23, find the value of y.

A.

-4

B.

-3

C.

-1

D.

2

Correct answer is B

\(P = begin{pmatrix} y - 2 & y - 1 \\ y - 4 & y + 2 \end{pmatrix}\)

\(|P| = (y - 2)(y + 2) - (y - 1)(y - 4) = (y^{2} - 4) - (y^{2} - 5y + 4) = -23\)

\(5y - 8 = -23 \implies 5y = -23 + 8 = -15\)

\(y = \frac{-15}{5} = -3\)

507.

Given that \(\frac{\mathrm d y}{\mathrm d x} = \sqrt{x}\), find y.

A.

\(2x^{\frac{3}{2}} + c\)

B.

\(\frac{2}{3}x^{\frac{3}{2}} + c\)

C.

\(\frac{3}{2}x^{\frac{3}{2}} + c\)

D.

\(\frac{2}{3}x^{2} + c\)

Correct answer is B

\(\frac{\mathrm d y}{\mathrm d x} = \sqrt{x} = x^{\frac{1}{2}}\)

\(y = \int x^{\frac{1}{2}} \mathrm {d} x\)

= \(\frac{x^{\frac{1}{2} + 1}}{\frac{1}{2} + 1} + c = \frac{x^{\frac{3}{2}}}{\frac{3}{2}} + c \)

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

508.

Find the range of values of x for which \(x^{2} + 4x + 5\) is less than \(3x^{2} - x + 2\)

A.

\(x > \frac{-1}{2}, x > 3\)

B.

\(x < \frac{-1}{2}, x > 3\)

C.

\(\frac{-1}{2} \leq x \leq 3\)

D.

\(\frac{-1}{2} < x < 3\)

Correct answer is B

No explanation has been provided for this answer.

509.

The fourth term of an exponential sequence is 192 and its ninth term is 6. Find the common ratio of the sequence.

A.

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

B.

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

C.

\(2\)

D.

\(3\)

Correct answer is B

\(T_{n} = ar^{n - 1}\)

\(T_{4} = ar^{4 - 1} = ar^{3} = 192\)

\(T_{9} = ar^{9 - 1} = ar^{8} = 6\)

Dividing \(T_{9}\) by \(T_{4}\), 

\(r^{8 - 3} = \frac{6}{192}\)

\(r^{5} = \frac{1}{32} = (\frac{1}{2})^{5}\)

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

510.

Differentiate \(x^{2} + xy - 5 = 0\)

A.

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

B.

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

C.

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

D.

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

Correct answer is A

\(\frac{\mathrm d}{\mathrm d x}(x^2 + xy - 5) = \frac{\mathrm d (x^{2})}{\mathrm d x} + \frac{\mathrm d (xy)}{\mathrm d x} - \frac{\mathrm d (5)}{\mathrm d x} = 0\)

= \(2x + x\frac{\mathrm d y}{\mathrm d x} + y = 0\)

\(\implies x\frac{\mathrm d y}{\mathrm d x} = -(2x + y)\)

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