Find the value of k if the triangle formed by A(8,10), B(7,3) and C(0,k) is right angled at B.
As B is a right angle, so, AC must be the hypotenuse and hence by
Pythagoras Theorem, AC2 = AB2 + BC2
Or, (0 – 8)2 + (k + 10)2 = (7 – 8)2+ (– 3 + 10)2 + (0 – 7)2 + (k +3)2
Or, 64 + k2 + 20k + 100 = 1 + 49 + 49 + k2 + 6k + 9
Or, 14k=108–164=–56Or,k=–5614=–4. [Ans.]