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JAMB Mathematics Past Questions & Answers - Page 142

706.

In this figure, PQRS is a parallelogram, PS = PT and < PST = 55o. The size of <PQR is

A.

125o

B.

120o

C.

115o

D.

110o

E.

10o

Correct answer is D

Both pairs of opp. angles are equal

< STP = 55o - isosceles angle

< TSR = 55o - alternate angle to < STP

Hence, < PSR = 55o + 55o = 110o

< PQR = 110^o

707.

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}

708.

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

709.

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}

710.

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