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