15.20 would be the tip
Hope this helps :)
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The vertex form is
f(x) = a(x - (-1))^2 - 108 = a(x + 1)^2 - 108 where a is some constant.
from the y intercept x = 0 when f(x) = -105, so substituting:-
-105 = a (0+1)^2 - 108
a = -105+108 = 3
so our equation is f(x) = 3(x + 1)^2 - 108
for x intercept:-
3(x +1)^2 - 108 = 0
(x + 1)^2 = 108 / 3 = 36
x+ 1 = +/- sqrt36 = +/- 6
x = -7 or 5
so the x intercepts are at ( (-7,0) and (5,0)