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WAEC Mathematics 2011 Paper

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Question : 42

Total: 47

The graph represents the relation y = x

^2

- 3x - 3. What is the equation of the line of symmetry of the graph?

y = 0.5
x = 1.0
x = 1.5
y = 4.6

Solution:

Concept:

For a quadratic expression

y = ax^2 + bx + c

, the axis of symmetry is

x = -\frac{b}{2a}

.

Explanation:

The given equation is

y = x^2 - 3x - 3

.

Compare it with

y = ax^2 + bx + c

.

Here,

a = 1

and

b = -3

.

Substitute these values into the formula:

x = -\frac{-3}{2(1)} = \frac{3}{2} = 1.5

Therefore, the line of symmetry is a vertical line at

x = 1.5

.

Answer:

C.

x = 1.5

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