Question

the two angles of triangle is a complemantry. find the third angle​

Answer 1

sum of the angles in a triangle is equal to 180 ° in question you given that two angles are complementary 90° ....
then third angle is a complementary angle I.e, 90°
(x + y = 180
90 + y = 180
y = 180-90
= 90)
hope it help

Answer 2

Let the 3 angles of the given triangle be A,B and C respectively.

Given that, two angles are complementary.

so, A+B=90°. ...(i)

By angle sum property of a triangle,

A + B + C = 180°

90° + C = 180°. { from (i) }

C = 90°

Therefore in a triangle if any two angles are complementary, the third angle will be 90°