Question

Explain why an angle that is supplementary to an acute angle must be an obtuse angle.

Answer 1

supplementary angles add up to 180 degrees.
if one is less than 90, the other angle must be greater than 90 in order to add up to 180 degrees

Answer 2

because they add up to 180 degrees so if one is acute the other must be > 90 degrees ie obtuse

Answer 3

So supplementary means that angles A + B = 180

So say that angle a is <90 degrees (acute)

Its supplement must therefore fill the rest of the 180, meaning it would have to be >90