Need help
The vertex of the graph of a quadratic function is (2, –1) and the y-intercept is (0, 7). Which of the following is the equation of the function?
A.
y=2x^2-8x+7
B.
y=2x^2+8x+7
C.
y=2x^2+8x-7
D.
y=2x^2-7x+8

Question

Need help
The vertex of the graph of a quadratic function is (2, –1) and the y-intercept is (0, 7). Which of the following is the equation of the function? 
A.
y=2x^2-8x+7
B.
y=2x^2+8x+7
C.
y=2x^2+8x-7
D.
y=2x^2-7x+8

anonymous · Answer

couple ways to do this
probably the easiest is to start with in in vertex form 
since the vertex is $(2,-1)$ it will be$$y=a(x-2)^2-1$$

anonymous · Answer

all you need is $a$ 
since $(0,7)$ is on the graph, put $x=0$ and $y=7$ solve 
$$7=a(0-2)^2-1$$ for $a$

anonymous · Answer

a=2