Question
In the given figure, ABCD is a parallelogram in which $\angle\text{BDC}=45^{\circ}$ and $\angle\text{BAD}=75^{\circ}.$ Then, $\angle\text{CBD}=?$

  1. 45°
  2. 55°
  3. 60°
  4. 75°

Answer

  1. 60°.

Solution:

Since ABCD is a parallelogram, AB || CD since opposite angles of a parallelogram are equal.

$\Rightarrow\angle\text{ABD}=\angle\text{BCD}=45^{\circ}$ ...(Alternate angles)

In $\triangle\text{ADB},$

$\angle\text{ABD}+\angle\text{BDA}+\angle\text{DAB}=180^{\circ}$ ...(Angle sum property)

$\Rightarrow45+\angle\text{BDA}+75=180$

$\Rightarrow\angle\text{BDA}+120=180$

$\Rightarrow\angle\text{BDA}=60^{\circ}$

$\Rightarrow\angle\text{CBD}=\angle\text{BDA}=60^{\circ}$ ...(Alternate angles)

$\Rightarrow\angle\text{CBD}=60^{\circ}$

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