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WAEC Mathematics 2017 Paper

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Question : 6

Total: 49

Given that a = log 7 and b =

\log

2, express log 35 in terms of a and b.

a + b + 1
ab - 1
a - b + 1
b - a + 1

Solution:

Concept:

Express

35

as a product or quotient of numbers whose logs are known:

7

,

2

, and

10

.

Explanation:

Given

a = \log 7

and

b = \log 2

(base

10

).

Write

35 = \frac{7 \times 10}{2}

.

So,

\log 35 = \log\left(\frac{7 \times 10}{2}\right)

.

Using logarithm laws:

\log 35 = \log 7 + \log 10 - \log 2

.

Since

\log 10 = 1

, substitute:

\log 35 = a + 1 - b

.

This can be written as

\log 35 = a - b + 1

.

Answer:

a - b + 1

(Option C).

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