General formula for interior angles of regular polygon with n sides
=(n−2n)×180∘
As we know Octagon has 8 sides, so n=8
Magnitude of interior angle in degrees
=(8−28)×180∘
=135∘
And, magnitude of interior angle in radians
=(8−28)×πc
[∵ 180∘=πc]
=(3π4)c
Hence, magnitude, in degrees and radians are 135∘, (3π4)c respectively.