Cos=0.985 rounded to nearest tenth

Actually Welcome to the Concept of the Graphs and plots,

since the given equation is a parabolic equation graph, hence we substitute every value to get the value of variable y.

1.) if x = -5 ,then 25-30-7 => y = -12

2.) if x = -1 , then 1-6-7 => y = -12

3.) if x = -6 , then 36 -36 -7=> y = -7

4.) if x = 0 , then 0+0-7 => y = -7

hence all values are proved above