Question

two angles of a triangle are complementary find the third angle

Answer 1

let the third angle be x
90 + x= 180( sum of all angles)
x=180-90
x=90

Answer 2

let a, b, c be three angles of triangle
given,a+b=90
a+b+c=180(asp)
90+c=180
c=180-90
c=90