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WAEC Further Mathematics 2017 Paper

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Question : 7

Total: 40

Given that

f(x) = \frac{x+1}{2}

f^{1}(-2)

.

-5
-3
$-\frac{1}{2}$
5

Solution:

Concept:

Find the inverse function, then substitute

x = -2

.

Explanation:

Let

y = f(x)

. Then:

y = \frac{x+1}{2}

Multiply both sides by 2:

2y = x + 1

Subtract 1 from both sides:

x = 2y - 1

Interchange

x

and

y

to get the inverse:

f^{-1}(x) = 2x - 1

Now substitute

x = -2

:

f^{-1}(-2) = 2(-2) - 1 = -4 - 1 = -5

Answer:

f^{-1}(-2) = -5

Option A.

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