WAEC Further Mathematics Past Questions & Answers - Page 102

506.

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

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

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

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

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

507.

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.

508.

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 \(T_{4}\), 

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

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

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

509.

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

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

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

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

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

510.

Find the equation of the line that is perpendicular to \(2y + 5x - 6 = 0\) and bisects the line joining the points P(4, 3) and Q(-6, 1)

A.

y + 5x + 3 = 0

B.

2y - 5x - 9 = 0

C.

5y + 2x - 8 = 0

D.

5y - 2x - 12 = 0

Correct answer is D

\(Line: 2y + 5x - 6 = 0\)

\(2y = 6 - 5x  \implies y = 3 - \frac{5x}{2}\)

Gradient = \(\frac{-5}{2}\)

For the line perpendicular to the given line, Gradient = \(\frac{-1}{\frac{-5}{2}} = \frac{2}{5}\)

The midpoint of P(4, 3) and Q(-6, 1) = \((\frac{-6 + 4}{2}, \frac{3 + 1}{2})\)

= (-1, 2).

Therefore, the line = \(\frac{y - 2}{x + 1} = \frac{2}{5}\)

\(2(x + 1) = 5(y - 2) \implies 5y - 2x - 12 = 0\)