First, the vertex

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Our vertex is at (5, 0)

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f(x) = -(2)|x - 5|

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If we try plugging in x  = 4 we get

f(x) = -(2)|4-5|

f(x) = (-2)(1)

f(x) = -2

y = -2

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If we try plugging in x = 6 we get

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f(x) = -(2)|6 - 5|

f(x) = -(2)(1)

f(x) = -2

y = -2

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So now we have two more points to our graph that we can confirm align.

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Taking this into consideration, we can label the graph's function as

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f(x) = -2|x-5|