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Find the value of the unknown interior angle x in the following figures:
"
To do:
We have to find the value of unknown interior angle $x$ in each case.
Solution:
For convenience, we shall name all the triangles given in the diagram as $\triangle ABC$.
We know that,
An exterior angle of a triangle is equal to the sum of its interior opposite angles.
Therefore,
(i) $\angle A+x=\angle ACD$
$\Rightarrow 50^{\circ}+\ x=115^{\circ}$
$\Rightarrow x=115^{\circ}-50^{\circ}$
$\Rightarrow x=65^{\circ}$
(ii) $\angle A+x=\angle CBD$
$\Rightarrow 70^{\circ}+\ x=100^{\circ}$
$\Rightarrow x=100^{\circ}-\ 70^{\circ}$
$\Rightarrow x=30^{\circ}$
(iii) $\angle C+x=\angle BAD$
$\Rightarrow 90^{\circ}+x=125^{\circ}$
$\Rightarrow x=125^{\circ}-\ 90^{\circ}$
$\Rightarrow x=35^{\circ}$
(iv) $\angle A+x=\angle ABD$
$\Rightarrow 60^{\circ}+\ x=120^{\circ}$
$\Rightarrow x=120^{\circ}-60^{\circ}$
$\Rightarrow x = 60^{\circ}$
(v) $\angle B+x=\angle CAD$
$\Rightarrow 30^{\circ}+\ x=80^{\circ}$
$\Rightarrow x=80^{\circ}-\ 30^{\circ}$
$\Rightarrow x=50^{\circ}$
(vi) $\angle B+x=\angle BCD$
$\Rightarrow 35^{\circ}+\ x=75^{\circ}$
$\Rightarrow x=75^{\circ}-35^{\circ}$
$\Rightarrow x=40^{\circ}$