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The axis of symmetry for the function [tex]f(x) = -x^2 - 10x + 16[/tex] is [tex]x = -5[/tex]. What are the coordinates of the vertex of the graph?

A. [tex](-5, 41)[/tex]
B. [tex](-5, 56)[/tex]
C. [tex](-5, 76)[/tex]
D. [tex](-5, 91)[/tex]


Sagot :

To determine the coordinates of the vertex of the function [tex]\( f(x) = -x^2 - 10x + 16 \)[/tex], we start with the information that the axis of symmetry is at [tex]\( x = -5 \)[/tex]. The vertex of a parabola given by a quadratic function [tex]\( ax^2 + bx + c \)[/tex] lies on its axis of symmetry. Here, since we already know that the axis of symmetry is [tex]\( x = -5 \)[/tex], the x-coordinate of the vertex is [tex]\(-5\)[/tex].

Next, we need to find the y-coordinate of the vertex by substituting [tex]\( x = -5 \)[/tex] into the function [tex]\( f(x) \)[/tex].

[tex]\[ f(-5) = -(-5)^2 - 10(-5) + 16 \][/tex]

Now calculate each term step-by-step:
[tex]\[ (-5)^2 = 25 \][/tex]
[tex]\[ -(-5)^2 = -25 \][/tex]
[tex]\[ 10(-5) = -50 \quad \text{so} \quad -10(-5) = 50 \][/tex]

Putting it all together:
[tex]\[ f(-5) = -25 + 50 + 16 \][/tex]

Simplify the result:
[tex]\[ -25 + 50 = 25 \][/tex]
[tex]\[ 25 + 16 = 41 \][/tex]

As a result, the y-coordinate of the vertex is [tex]\( 41 \)[/tex]. Therefore, the coordinates of the vertex are [tex]\( (-5, 41) \)[/tex].

From the given options, the correct answer is:
[tex]\[ (-5, 41) \][/tex]