2n-4×90°=3×360°n×n⇒n-2×180=3×360⇒n-2=6∴ n=8

Pl solve. It

Pl solve. It 74. If the sum of interior angles of a polygon is 3 times the sum of its exterior angles, then the number of sides of the polygon is (3) 10 (4) 12

\{(2 n - 4) \times 90 °\} = 3 \times (\frac{360 °}{n} \times n) \Rightarrow (n - 2) \times 180 = 3 \times 360 \Rightarrow n - 2 = 6 ∴ n = 8