JAMB Mathematics Past Questions & Answers - Page 358

1,786.

Find the angle subtended at the center of a circle by a chord which is equal in length to the radius of the circle.

30^o

45^o

60^o

90^o

Correct answer is C

If a length of a chord is equal to the length of a radius in the same circle, the triangle formed y the chord and the radii is an equilateral triangle
∴each angle = 60o

1,787.

Find the exterior angle of a 12 sided regular polygon

12^o

24^o

25^o

30^o

View answer & explanation

Correct answer is D

Exterior angle = 360 / n
= 360 / 12
= 30o

1,788.

A binary operation on the real set of numbers excluding -1 is such that for all m, n ∈ R, mΔn = m+n+mn. Find the identity element of the operation.

zero

-¹/₂

-1

View answer & explanation

Correct answer is B

mΔn = m+n+mn
Let e be the identity element
∴mΔe = eΔm = m
m+e+me = m
e+me = m-m
e+me = 0
e(1+m) = 0
e = 0 / (1+m)
e = 0

1,789.

A binary operation * is defined on the set of positive integers is such x*y = 2x-3y+2 for all positive integers x and y. The binary operation is?

commutative and close on the set of positive integers

neither commutative nor closed on the set of positive integers

commutative but not closed on the set of positive integers

not cummutative but closed on the set of positive integers

View answer & explanation

Correct answer is B

X * Y = 2X - 3Y + 2
2*3 = 2(2) - 3(3) + 2
=4-9+2
= -3
But -3 does not belong to positive integer

1,790.

The fifth term of an A.P is 24 and the eleventh term is 96. Find the first term.

-12

-24

View answer & explanation

Correct answer is D

U5 = 24, n = 5 and U11 = 96, n = 11
Un = a + (n-1)d
24 = a + (5-1)d imply 24 = a+4d .....eqn1
96 = a + (11-1)d imply 96 = a+10d ...eqn2
eqn1 - eqn2 -72 = -6d
d = 72/6 = 12
but 24 = a+4d
24 = a + 4(12)
24 = a + 48
a = 24-48
a = -24