WAEC Mathematics Past Questions & Answers - Page 137

681.

Each of the interior angles of a regular polygon is 140o. Calculate the sum of all the interior angles of the polygon

A.

1080o

B.

1260o

C.

1800o

D.

2160o

Correct answer is B

Each interior angle = 140

\(\frac{(n - 2) \times 180}{n} = 140\)

(n - 2) x 180 = 140n

150 - 360 = 140n

180m - 140n = 360

40n - 360

n = \(\frac{360}{40}\)

n = 9

Sum of all interior angles = (n - 2) x 180

= (9 - 2) x 180

= 7 x 180

= 1260

682.

If c and k are the roots of 6 - x - x2 = 0, find c + k

A.

2

B.

1

C.

-1

D.

-3

Correct answer is C

6 - x - x2 = 0

a = -1; b = -1; c = 6

Sum of roots = c + k = -\(\frac{-b}{a}\)

= \(\frac{-(-1)}{-1}\)

= -1

683.

If a positive integer, list the values of x which satisfy the equation 3x - 4 < 6 and x - 1 > 0

A.

{1, 2, 3}

B.

{2, 3}

C.

{2, 3, 4}

D.

{2, 3, 4, 5}

Correct answer is B

3x - 4 < 6 = 3x < 6 = 4

3x < 10

x < \(\frac{10}{3}\)

x < 3.33 and x - 1 = 0

n > 1 = 1< x; since x is an integer, and 1 < x3.33

x = {2, 3}

684.

solve \(\frac{2x + 1}{6} - \frac{3x - 1}{4}\) = 0

A.

1

B.

\(\frac{1}{5}\)

C.

-\(\frac{1}{5}\)

D.

-1

Correct answer is A

\(\frac{2x + 1}{6} - \frac{3x - 1}{4}\) = 0

\(\frac{4(2n + 1) - 6(3x - 1)}{24}\) = 0

-10x + 10 = 0

-10x = -10

x = \(\frac{-10}{-10}\)

x = 1

685.

An arc of a circle subtends an angle of 60o at the centre. If the radius of the circle is 3cm, find , in terms of \(\pi\), the length of the arc

A.

\(\pi\)cm

B.

2\(\pi\)cm

C.

3\(\pi\)cm

D.

6\(\pi\)cm

Correct answer is A

Length of arc = \(\frac{\theta}{360} \times 2\pi r\)

= \(\frac{60}{360} \times 2\pi \times 3cm\)

= \(\pi\)cm