Question

△PQR has three sides as PQ = 25 units, QR = 20 units, and PR = 15 units. So, the largest angle in the triangle is .

• A. 90°
• B. 180°
• C. 100°
• D. 45°

Answer 1

The correct option is A 90°

Given, sides of the triangle are 3 cm, 4 cm and 5 cm.

PQ = 25 units;
QR = 20 units, and
PR = 15 units.

Arranging the sides in ascending order, we get: 15 < 20 < 25.

So, longest side is 25 units.

We know,
${15}^2+{20}^2=225+400=625={25}^2$

By the converse of Pythagoras' theorem, if in a triangle, the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides., then the triangle is right-angled.

Thus, △PQR is a right-angled triangle, and hence, its greatest angle is 90°.