Question

If sum of two angles of a triangle is ${60}^o$. Then, the measure of third angle of a triangle is:

• A. ${60}^o$
• B. ${90}^o$
• C. ${120}^o$
• D. ${180}^o$

Answer 1

The correct option is C ${120}^o$

Let the angles be $x,y$ and $z$

Sum of two angles $=x+y$

Given $x+y={60}^{\circ }$

Using angle sum property

$x+y+z={180}^{\circ }$

${60}^{\circ }+z={180}^{\circ }$

$z={120}^{\circ }$