JAMB Mathematics Past Questions & Answers - Page 147

731.

In the figure, \(\bigtriangleup\) ABC are in adjacent planes. AB = AC = 5cm, BC = 6cm and o then AE is equal to

A.

3\(\sqrt{2}\)

B.

2\(\sqrt{3}\)

C.

\(\frac{\sqrt{3}}{2}\)

D.

\(\frac{2}{\sqrt{3}}\)

Correct answer is B

BC = 6 : DC = \(\frac{6}{2}\) = 3cm

By construction < EDE = 180o(90o + 60o) = 180o - 150o

= 30o(angle on a strt. line)

From rt < triangle ADC, AD2 = 52 - 32

= 25 - 9 = 6

AD = 4

From < AEC, let AS = x

\(\frac{x}{sin 60^o}\) - \(\frac{4}{sin 90^o}\)

sin 90o = 1

sin 60o = \(\frac{\sqrt{3}}{2}\)

x = 4sin 60o

x = 3 x \(\frac{\sqrt{3}}{2}\)

= 2\(\sqrt{3}\)

732.

In the figure, 0 is the centre of the circle ABC, < CED = 30o, < EDA = 40o. What is the size of < ABC?

A.

70o

B.

110o

C.

130o

D.

125o

E.

145o

Correct answer is D

If < CED = 30º, and < EDA = 40º then

<EOD = 180-(30-40) (angles in a triangle sum to 180) → 110º

<AOC = <EOD = 110º

At centre O: 360 - 110 = 250º

The angle subtended by an arc of a circle at its center is twice the angle it subtends anywhere on the circle's circumference.

250 * \(\frac{1}{2}\) → 125º

<ABC = 125º

733.

In the Figure FD\\AC, the area of AEF = 6sq.cm. AE = 3cm, BC = 3cm, CD = 5cm, < BCD is an obtuse angle. Find the length of BD.

A.

\(\sqrt{33}\)

B.

6

C.

4

D.

2\(\sqrt{13}\)

E.

4\(\sqrt{5}\)

Correct answer is D

Area of triangle AEF = 6sq. cm

area of triangle = \(\frac{1}{2}\)bh (Line DX makes right angles with the parallel lines)

6 = \(\frac{1}{2}\) x 3 x h

6 = 3h

3h = \(\frac{12}{3}\)

h = 4 = DX

From D, C x D, CX2 = 52
- 42

= 25 - 16 = 9

Cx = 3. From angle B x D, Bx = 6(i.e. 3 + 3)

BD2 = 42 + 62


= 16 + 36 = 52

BD = \(\sqrt{4 \times 13}\)

= 2\(\sqrt{13}\)

734.

In the figure, AB is parallel to CD then x + y + z is

A.

185o

B.

200o

C.

270o

D.

360o

E.

195o

Correct answer is D

x + y + z = 360o

735.

In the figure, DE//BC: DB//FE: DE = 2cm, FC = 3cm, AE = 4cm. Determine the length of EC.

A.

4cm

B.

6cm

C.

3cm

D.

2cm

E.

1cm

Correct answer is B

Angles ADE and EFC are similar,
Therefore,

= \(\frac{x}{3} = \frac{4}{2}\)

= \(\frac{x}{3} = 2\)

x = 3 x 2 = 6