Given :
The diagonals of rhombus ABCD intersect at E.
∠CAD = 20°.
To Find :
The angle ∠CDA.
Solution :
We know, diagonals of a rhombus bisects each other perpendicularly.
So, ∠DEA = 90°.
In triangle ΔEAD :
∠EAD + ∠AED + ∠EDA = 180°
20° + 90° + ∠EDA = 180°
∠EDA = 70°
Now, we know diagonal of rhombus also bisect the angle between two sides .
So, ∠CDA = 2∠EDA
∠CDA = 2×70°
∠CDA =140°
Therefore, ∠CDA is 140°.