The equation of a circle is (x + 6)2 + (y - 4)2 = 16. the point (-6, 8) is on the circle.

what is the equation of the line that is tangent to the circle at (-6, 8)?

y = 8
x = 8
x = -2
y = 0

The answer is y = 0 

If you look that the formula of the circle,  you can see that the center of the circle is (-6, 4). If you sketch a graph and plot that point and then you plot (-6,8) you can see that it lands directly on top of it. Since the line is vertical from it, the slope is 0, causing the equation of the line to be y=0