一等差數列前三項合30且前三項平方合332,公差d為正數求d
回答 (1)
2012-03-20 9:16 am
✔ 最佳答案
(a - d) + a + (a + d) = 30{
(a - d)² + a² + (a + d)² = 332==>a = 10
{
(10 - d)² + 10² + (10 + d)² = 332
(100 - 20d + d²) + 100 + (100 + 20d + d²) = 332
300 + 2d² = 332
d² = 16d = 4 或 - 4(捨)
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