Answer :
We have the expressions:
[tex]f(x)=x^2+6x+15[/tex][tex]y=x^2-4x+9[/tex][tex]f(x)=x^2-8x[/tex][tex]y=x^2+7x-2[/tex]Now, with this we operate as follows:
a)
[tex]f(x)=x^2+6x+15=x^2+6x+9+15-9[/tex][tex]\Rightarrow(x+3)^2+6[/tex]Then, the axis is x = -3 and the vertex (-3, 6)
b)
[tex]y=x^2-4x+9=x^2-4x+4+9-4[/tex][tex]\Rightarrow(x-2)^2+5[/tex]Then, the vertex is (2, 5) and the axis is x = 2.
c)
[tex]f(x)=x^2-8x+4-4\Rightarrow(x-2)^2-4[/tex]Then, the vertex is (2, -4) andd the axis is x = 2.
d)
[tex]y=x^2+7x-2=x^2+7x+\frac{49}{4}-2-\frac{49}{4}[/tex][tex]\Rightarrow(x+\frac{7}{2})^2-\frac{57}{4}[/tex]Then, the vertex is (-7/2, -57/4) and the axis is -7/2.