Question

ABCD is a square,BD is diagonal.Find the measure of ∠CDB

Answer 1

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Answer 2

ABCD is square
with diagonal DC

In triangle DAB and triangle DCB
DA=DC (side of square)
AB=CB (side of square)
DB=DB (common)

So
By SSS rule
triangle DAB is congurent to triangle DCB

By
CPCT
Angle CDB = Angle ADB......1

Angle ADC = 90° ( Angle of square)
angle CDB + angle ADB = 90° ( Angle ADC = angle CDB + angle ADB )
by eqn 1
angle CDB + angle CDB = 90°
2 angle CDB = 90°
angle CDB = 90/2
angle CDB = 45°
hence proved