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What is the axis of symmetry of the function f(x)=-(x+9)(x-21)

User Seanmk
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2 Answers

5 votes

Answer:

x=6

Explanation:

did it on edge

User Thinlizzy
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Carry out the mult.: f(x) = -[x^2 - 21x + 9x - 189]

Combine like terms: f(x) = -[x^2 - 12x - 189]
Eliminate the brackets [ ]: f(x) = -x^2 + 12x + 189
Identify coefficients a, b and c: a= -1, b=12, c=189

The equation of the axis of symmetry is x = -b/(2a), which here equals

x = -(12)/[2(-1)], or x = 6

This is also the x-coordinate of the vertex. Plug x=6 into the original equation to calculate the y-coordinate.
User FireEmerald
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