Question

Write the type of triangle for each of the descriptions given below.

(1) In ∆ABC, m∠A = 63°, m∠B = 52° and m∠C = 65°
(2) In ∆RST, seg RS and seg ST are equal.
(3) In ∆LMN, ∠LNM is a right angle.
(4) In ∆SDO, the measure of ∠OSD is 135°.
(5) All three sides of ∆RTO are of equal length.
(6) The sides of ∆DEF are 5.3 cm, 4.2 cm and 6.6 cm.

Answer 1

(1) Since the measures of all angles of ∆ABC are less than 90°,
it is an acute angled triangle.

(2) Since the two sides ST and RS of ∆RST are equal, it is an isosceles triangle.

(3) It is given that ∠LNM = 90°.
Since one angle of ∆LMN is a right angle, it is a right-angled triangle.

(4) It is given that ∠OSD = 135°.
Since, 135° > 90°, ∆OSD is an obtuse angled triangle.

(5) Since all the three sides of ∆RTO are equal, it is an equilateral triangle.

(6) It can be observed that all the three sides of ∆DEF are unequal. So, ∆DEF is a scalene triangle.