Question

Given that two angles of triangle A are ${50}^o\&{40}^o$ and two angles of triangle B are ${65}^o\&{20}^o$.
Which of the following is/are correct?

• A. Triangle A is an acute angled triangle.
• B. Trinagle B is an obtuse angled triangle.
• C. Triangle A is a right-angled triangle.
• D. Triangle B is a acute angled triangle.

Answer 1

Answer: (B), (C)

Triangle A is a right-angled triangle.

Given that two angles of triangle A are ${50}^o\&{40}^o$
Using interior angle sum property
We know: Sum of three angles of the triangle is ${180}^o$
Hence, third angle of the triangle is ${180}^o-{50}^o-{40}^o={90}^o$
Triangle A is a right-angled triangle.

third angle of triangle B is ${180}^o-{65}^o-{15}^o={100}^o$
$\because {100}^o>{90}^o$
Triangle B is an obtuse angled triangle.