Let P(-7, 7) cut the interval AB in the ratio m:n.
-7 = [(-2)n + 3m]/(m + n)
-7(m + n) = -2n + 3m
-7m - 7n = -2n + 3m
-10m = 5n
m/n = -5/10
m/n = -1/2
Therefore, the point cuts the interval in the ratio -1:2
The reason why you only need to do it once is because you're finding the ratio between intervals, which can be rewritten in fractional form.