Answer:
...F(x)=x² +18x +81 find the vertex
a=1, b=18, c=81
apply the formula -b/2a = -18/2= -9
x coordinate of vertex =-9
calculate y coordinate :
replace x in f(x) :
(-9)²+18*-9 +81 = 81-162+81=0
The y-coordinate =0
the vertex of the function f(x)=x²+18x+81 is (-9,0)
Explanation: