The function is undefinded if the denominator, x-5, equals 0.
So

.
The domain is

.
In interval notation, this is (-infinity, 5) u (5, infinity).
The answer would be (5, -2). This is because when you plug in the respective values in for x and y into the equation 3x - 3y = 21, you get 21, which is the desired answer.
3x - 3y = 21
3(5) - 3(-2) = 21
15 + 6 = 21
21 = 21
Hope this helped!
I think you meant to add more to your question (posting the specific problem).
In general, one special right triangle is the <span>45°-45°-90° triangle, in which both legs are congruent and the hypotenuse = √2 * the length of the leg. if you happen to not have the length of the leg, the formula for finding the leg is: leg = hypotenuse / √2
Another special right triangle is the </span><span>30°-60°-90° triangle. With this kind of triangle the length of the hypotenuse is twice the length of the shorter leg. The length of the longer leg is √3 times the length of the shorter leg.
hypotenuse = 2 * shorter leg
longer leg = √3 * shorter leg</span>
the answer to your question is n = -2