Sum of inner angles

Prove that the sum of all inner angles of any convex n-angle equals (n-2) . 180 degrees.

Correct answer:

d =  0

Step-by-step explanation:

$$\begin{gathered} n=3\dots s_3=180^{\circ } \\ n=4\dots s_4=s_3+180^{\circ } \\ n=5\dots s_5=s_4+180^{\circ } \\ s=180n-360=180(n-2) \\ d=0 \end{gathered}$$

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