From (1), (2), (3)
(∴ By Pythagoras theorem, in a right angled triangle square of hypotenuse is equal to sum of the squares of other two side)
And also in the figure, ∆ADC, ∆DBC are two other triangles.
As per the data given,
92 + 122 = 81 + 144 = 225 = 152
∴ ∆ ADC is a right angled triangle, then 122 + 162
= 144 + 256 = 400 = 202
∴ ∆ DBC is also a right angled triangle