We call A(–3, 5), B(4, –1), and C(4, y), the triangle ABC.
We have the coordinates of three vectors: AB(7, -6), BC(0; y+1), and AC(7, y-5)
Cause this triangle can be right at A, B or C, we have three cases:
+ Right at A: AB.AC=0 or 7x7+(-6)x(y-5)=0
and we have 49-6y+30=0 or y=79/6
+ Right at B: AB.BC=0 or 7x0+(-6)x(y+1)=0
and we have 0-6y-6=0 or y=-1
Right at C: BC.AC=0 or 0x7+(y+1)x(y-5)=0
and we have (y+1)x(y-5)=0 or y=-1 or y=5
Then, we have 3 values of y.
