WAEC Mathematics Past Questions & Answers - Page 25

121.

if tanθ = \(frac{3}{4}\), 180° < θ < 270°, find the value of cosθ.

A.

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

B.

\(\frac{3}{5}\)

C.

-\(\frac{4}{5}\)

D.

-\(\frac{3}{5}\)

Correct answer is C

tanθ = \(frac{3}{4}\) → tanθ = 0.75

θ = tan\(^{-1}\)[0.75] → 36.8698°

cosθ = cos[36.8698°] 

→ 0.800 or  \(frac{4}{5}\) 

However; in the third quadrant Cosine is negative

i.e -\(frac{4}{5}\) 

122.

Find The quadratic Equation Whose Roots Are -2q And 5q. 

A.

3x\(^2\) + 3qx - 10q\(^2\)

B.

x\(^2\) + 3qx + 10q\(^2\)

C.

x\(^2\) - 3qx + 10q\(^2\)

D.

x\(^2\) - 3qx - 10q\(^2\)

Correct answer is D

x\(^2\) - (sum of roots)x + (products of roots) = 0

x\(^2\) - (-2q + 5q) + (-2q * 5q) = 0

x\(^2\) -(3q) + (-10q\(^2\)) = 0

x\(^2\) -3q - 10q\(^2\) = 0

124.

In △LMN, |LM| = 6cm, ∠LNM = x and sin x = sin x = \(\frac{3}{5}\).

Find the area of △LMN 

A.

60cm\(^2\)

B.

48cm\(^2\)

C.

24cm\(^2\)

D.

30cm\(^2\)

Correct answer is C

No explanation has been provided for this answer.

125.

The height of an equilateral triangle of side is 10 3√ cm. calculate its perimeter.

A.

20cm

B.

60cm

C.

40cm

D.

30cm

Correct answer is B

Height of an equilateral triangle, h = a\(\frac{√3}{2}\), where a is the side of the equilateral triangle.

10√3 = a\(\frac{√3}{2}\)

cross multiply--> 2 * 10√3 = a√3

√3 strikes √3 on both sides

20 = a

The perimeter of an equilateral triangle is: P = 3a

P = 3 * 20 = 60cm

P = 30√3