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What is the minimum value of the function g(x) = x^2 - 6x - 12?

A: -21

B: 3-√21

C: 3

D:3+ √21​


Sagot :

Answer:

A: -21

Step-by-step explanation:

Vertex of a quadratic function:

Suppose we have a quadratic function in the following format:

[tex]f(x) = ax^{2} + bx + c[/tex]

It's vertex is the point [tex](x_{v}, y_{v})[/tex]

In which

[tex]x_{v} = -\frac{b}{2a}[/tex]

[tex]y_{v} = -\frac{\Delta}{4a}[/tex]

Where

[tex]\Delta = b^2-4ac[/tex]

If a<0, the vertex is a maximum point, that is, the maximum value happens at [tex]x_{v}[/tex], and it's value is [tex]y_{v}[/tex].

In this question:

Quadratic function:

[tex]g(x) = x^2 - 6x - 12[/tex]

So [tex]a = 1, b = -6, c = -12[/tex].

Minimum value:

This is the y-value of the vertex. So

[tex]\Delta = b^2-4ac = (-6)^2 - 4(1)(-12) = 36+48 = 84[/tex]

[tex]y_{v} = -\frac{\Delta}{4a} = -\frac{84}{4} = -21[/tex]

The minimum value is -21, and the correct answer is given by option A.