Let us show that the points (7, 9), (3, –7) and (–3, 3) are the vertices of a right angled triangle by calculation.
Let A → (7, 9)
B → (3, -7)
C → (-3, 3)
be the vertices of a triangle.
We know that distance between two points (x1, y1) and (x2, y2) is given by 
.
Using the above distance formula,
AB 
BC 
CA 
Now, (BC)2 + (CA)2
and (AB)2
We find that (BC)2 + (CA)2 = (AB)2
Hence the points (7, 9), (3, –7) and (–3, 3) are the vertices of a right angled triangle.
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