#1**0 **

The sum of the internal angles of an n-sided polygon is given by 180^{o} • (n – 2)

So for an octagon (8 sides) the sum of its internal angles equals 180^{o} • (8 – 2)

Doing the arithmetic, this sum is 1,080^{o}

Since it is a regular octagon, all internal angles are equal, so each one is 135^{o}

x is a supplementary angle of one of those 135^{o} angles, so it equals 180^{o} – 135^{o}

Thus, **x = 45 ^{o}**

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Guest Nov 25, 2021