please answer 1,2 and 3!! Thank you

Answer:
1. The constant term is 16
[tex]f(x) = {x}^{2} + 8x + 16 - 16- 15[/tex]
2.
[tex]f(x) =( {x}^{2} + 8x + 16 )- 16- 15[/tex]
3.
[tex]f(x) = {(x + 4)}^{2} - 31[/tex]
Step-by-step explanation:
The given quadratic trinomial is
[tex]f(x) = {x}^{2} + 8x - 15[/tex]
The coefficient of x is 8. Half of 8 is 4.
The square of 4 is 16.
We add and subtract 16 to get;
[tex]f(x) = {x}^{2} + 8x + 16 - 16- 15[/tex]
The first three terms make a perfect square:
[tex]f(x) =( {x}^{2} + 8x + 16 )- 16- 15[/tex]
We now factor the perfect square and collect like terms to get:
[tex]f(x) = {(x + 4)}^{2} - 31[/tex]
This is called the vertex form.