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What is the vertex and axis of symmetry of f(x) = (x + 3)(x + 5)?

A vertex (-4, -1) & axis of symmetry x = -1

B vertex (-4, -1) & axis of symmetry x = -4

C vertex (4, 1) & axis of symmetry x = 4

D vertex (-4, 1) & axis of symmetry x = -4

Please need help on this

Respuesta :

If you expand y=(x+3)(x+5)
You get: f(x)= x^2+8x+15

A=1 b=8 C=15

To find x-coordinate of vertex:
use formula -b/2a
-8/2(1)= -4 this is x coordinate

To find y coordinate plug the x value in original equation.

F(-4) = (-4+3)(-4+5)
F(-4) = (-1)(1)
F(-4) = -1

Vertex is (-4, -1)

And x-coordinate of the vertex is the equation of the axis of symmetry of the parabola.

Axis of symmetry is -4

Option B is answer


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