Find the x intercepts of the parabola with vertex (-1,-16) and y intercept (0,-15)

 first, write the equation of the parabola in the required form: 
(y - k) = a·(x - h)² 

Here, (h, k) is given as (-1, -16). 
So you have: 
(y + 16) = a · (x + 1)² 

Unfortunately, a is not given. However, you do know one additional point on the parabola: (0, -15): 

-15 + 16 = a· (0 + 1)² 
.·. a = 1 

.·. the equation of the parabola in vertex form is 
y + 16 = (x + 1)² 

The x-intercepts are the values of x that make y = 0. So, let y = 0: 

0 + 16 = (x + 1)² 
16 = (x + 1)² 

We are trying to solve for x, so take the square root of both sides - but be CAREFUL! 

± 4 = x + 1 remember both the positive and negative roots of 16 

Solving for x: 
x = -1 + 4, x = -1 - 4 
x = 3, x = -5. 

Or, if you prefer, (3, 0), (-5, 0).