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WAEC Mathematics 2016 Paper

Question : 10

Total: 49

\frac{y^2 - 9y + 18}{y^2 + 4y - 21}

is undefined

Solution:

Concept:

A rational expression is undefined when its denominator equals zero.

Explanation:

The given expression is

\frac{y^2 - 9y + 18}{y^2 + 4y - 21}

To find where it is undefined, set the denominator to zero:

y^2 + 4y - 21 = 0

Factorize the quadratic:

y^2 + 7y - 3y - 21 = 0

y(y + 7) - 3(y + 7) = 0

(y - 3)(y + 7) = 0

Therefore,

y - 3 = 0

y + 7 = 0

So,

y = 3

y = -7

Answer:

The expression is undefined for

y = 3

y = -7

Correct option: C.

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