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The interior angles of a polygon are in arithmetic progression. The smallest angle is `120^@` and the common difference is `5^@` Find the number of sides of the polygon |
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Answer» Correct Answer - 9 Since, angle of polygon are in an AP. `:.` Sum of all angles `= (n -2) xx 180^(@) = (n)/(2) {2(120^(@)) + (n _1) 5^(@)}` `rArr 5n^(2) - 125 n + 720 = 0` `rArr n^(2) - 25n + 144 = 0` `rArr (n -9) (n-16) = 0` `rArr n = 9, 16` If n = 9, then largest angle `= a + 8d = 160^(@)` Again, if n = 16, then n largest angle `= a + 15d = 120^(@) + 75 = 195^(@)` Which is not possible. [since, any angle of polygon cannot be `gt 180^(@)`] Hence, n = 9 [neglecting n = 16] |
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