For this case we have that the sum of the angles of a triangle is equal to 180 degrees.
We have then:
[tex] x + y + z = 180
[/tex]
Where,
x, y, z: angles of the triangle
If one of the angles is equal to 90 degrees, we have:
[tex] x + y + 90 = 180
[/tex]
Clearing we have:
[tex] x + y = 180 - 90
x + y = 90
[/tex]
Answer:
if z = 90 then,
[tex] x + y = 90 [/tex]
