WAEC Further Mathematics Past Questions & Answers - Page 118

586.

A line passes through the origin and the point \((1\frac{1}{4}, 2\frac{1}{2})\). Find the y-coordinate of the line when x = 4.

A.

2

B.

4

C.

6

D.

8

Correct answer is D

The gradient of the equation = \(\frac{y_{1} - y_{0}}{x_{1} - x_{0}} = \frac{\frac{5}{2} - 0}{\frac{5}{4} - 0}\)

= \(\frac{\frac{5}{2}}{\frac{5}{4}} = 2\)

The line passes through the origin, therefore the equation of the line is y = mx

\(y = 2x\)

When x = 4, y = 2 x 4 = 8.

587.

A line passes through the origin and the point \((1\frac{1}{4}, 2\frac{1}{2})\), what is the gradient of the line?

A.

1

B.

2

C.

3

D.

4

Correct answer is B

\(Gradient = \frac{y_{1} - y_{0}}{x_{1} - x_{0}}\)

Line passing through \((0, 0)\) & \((1\frac{1}{4}, 2\frac{1}{2})\),

\(Gradient = \frac{2\frac{1}{2} - 0}{1\frac{1}{4} - 0} = \frac{\frac{5}{2}}{\frac{5}{4}} \)

588.

Find the minimum value of \(y = x^{2} + 6x - 12\).

A.

-21

B.

-12

C.

-6

D.

-3

Correct answer is A

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

\(\frac{\mathrm d y}{\mathrm d x} = 2x + 6 = 0\)

\(2x = -6 \implies x = -3\)

\(y(-3) = (-3)^{2} + 6(-3) - 12 = 9 - 18 - 12 = -21\)

589.

If \(36, p, \frac{9}{4}, q\) are consecutive terms of an exponential sequence (G.P.). Find the sum of p and q.

A.

\(\frac{9}{16}\)

B.

\(\frac{81}{16}\)

C.

\(9\)

D.

\(9\frac{9}{16}\)

Correct answer is D

\(T_{n} = ar^{n-1}\) (for an exponential sequence)

\(T_{1} = 36 = a\)

\(T_{2} = ar = 36r = p\)

\(T_{3} = ar^{2} = 36r^{2} = \frac{9}{4}\)

\(T_{4} = ar^{3} = 36r^{3} = q\)

\(36r^{2} = \frac{9}{4} \implies r^{2} = \frac{\frac{9}{4}}{36} = \frac{1}{16}\)

\(r = \sqrt{\frac{1}{16}} = \frac{1}{4}\)

\( p = 36 \times \frac{1}{4} = 9 ; q = \frac{9}{4} \times \frac{1}{4} = \frac{9}{16}\)

\(p + q = 9 + \frac{9}{16} = 9\frac{9}{16}\) 

590.

Given that \(f : x \to \frac{2x - 1}{x + 2}, x \neq -2\), find \(f^{-1}\), the inverse of f

A.

\(f^{-1} : x \to \frac{1+2x}{2-x}, x \neq 2\)

B.

\(f^{-1} : x \to \frac{1-2x}{x+2}, x \neq -2\)

C.

\(f^{-1} : x \to \frac{1-2x}{x-2}, x \neq 2\)

D.

\(f^{-1} : x \to \frac{1+2x}{x+2}, x \neq -2\)

Correct answer is A

\(f(x) = \frac{2x - 1}{x + 2}\)

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

\(x = \frac{2y - 1}{y + 2} \implies x(y + 2) = 2y - 1\)

\(xy - 2y = -1 - 2x  \implies y = \frac{-1 - 2x}{x - 2}\)

\(f^{-1} : x \to \frac{1 + 2x}{2 - x} ; x \neq 2\)