WAEC Further Mathematics Past Questions & Answers - Page 61

301.

Given that \(f '(x) = 3x^{2} - 6x + 1\) and f(3) = 5, find f(x).

A.

\(f(x) = x^{3} - 3x^{2} + x + 20\)

B.

\(f(x) = x^{3} - 3x^{2} + x + 31\)

C.

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

D.

\(f(x) = x^{3} - 3x^{2} + x - 13\)

Correct answer is C

\(f ' (x) = 3x^{2} - 6x + 1\)

\(f(x) = \int (3x^{2} - 6x + 1) \mathrm {d} x\)

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

\(f(3) = 5 = 3^{3} - 3(3^{2}) + 3 + c\)

\(27 - 27 + 3 + c = 5 \implies 3 + c = 5\)

\(c = 2\)

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

302.

The coefficient of the 5th term in the binomial expansion of \((1 + kx)^{8}\), in ascending powers of x is \(\frac{35}{8}\). Find the value of the constant k.

A.

2

B.

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

C.

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

D.

-2

Correct answer is B

\((1 + kx)^{8} = ^{8}C_{0}(1^{8})(kx)^{0} + ^{8}C_{1}(1^{7})(kx)^{1} + ...\)

The 5th term = \(^{8}C_{5 - 1}(1^{4})(kx)^{4}\)

= \(^{8}C_{4} (kx)^{4}\)

\(\implies 70k^{4} = \frac{35}{8}\)

\(k^{4} = \frac{\frac{35}{8}}{70}\)

\(k^{4} = \frac{1}{16}\)

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

303.

Find the derivative of \(3x^{2} + \frac{1}{x^{2}}\)

A.

\(6x + 2x^{2}\)

B.

\(6x + \frac{1}{2x}\)

C.

\(6x - \frac{2}{x^{3}}\)

D.

\(6x - \frac{1}{2x}\)

Correct answer is C

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

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

= \(6x - \frac{2}{x^{3}}\)

304.

A binary operation ,*, is defined on the set R, of real numbers by \(a * b = a^{2} + b + ab\). Find the value of x for which \(5 * x = 37\)

A.

7

B.

2

C.

-2

D.

-7

Correct answer is B

\(a * b = a^{2} + b + ab\)

\(5 * x = 5^{2} + x + 5x = 37\)

\(25 + 6x = 37 \implies 6x = 12\)

\(x = 2\)

305.

Find the locus of points which is equidistant from P(4, 5) and Q(-6, -1).

A.

3x - 5y + 13 = 0

B.

3x - 5y - 7 = 0

C.

5x - 3y + 7 = 0

D.

5x + 3y - 1 = 0

Correct answer is D

Midpoint between P(4, 5) and Q(-6, -1) = \(\frac{4 - 6}{2}, \frac{5 - 1}{2} = (-1, 2)\)

Gradient of PQ = \(\frac{5 - (-1)}{4 - (-6)} = \frac{3}{5}\)

Gradient of line perpendicular to PQ = \(\frac{-1}{\frac{3}{5}} = -\frac{5}{3}\)

\(line = \frac{y - 2}{x + 1} = \frac{-5}{3}\)

\(3y - 6 = -5x - 5\)

\(5x + 3y - 6 + 5 = 0 \implies 5x + 3y - 1 = 0\)