MQ12 --- Trigonometry
回答 (3)
2012-05-20 8:26 pm
✔ 最佳答案
(2cos²x - 1)/(cosx - sinx)= cos²x - (1 - cos²x ) / (cosx - sinx)
= cos²x - sin²x / (cosx - sinx)
= (cosx + sinx) (cosx - sinx) / (cosx - sinx)
= cosx + sinx
2012-05-21 5:28 am
他是說
因為2cos²x - 1 = cos²x-sin²x,
(2cos²x - 1)/(cosx - sinx) = (cos²x-sin²x)/(cosx - sinx)
再把分母及分子乘以(cos x + sin x),分母變成cos²x-sin²x,同分子約左,
所以得出答案cosx+sinx
因為2cos²x - 1 = cos²x-sin²x,
(2cos²x - 1)/(cosx - sinx) = (cos²x-sin²x)/(cosx - sinx)
再把分母及分子乘以(cos x + sin x),分母變成cos²x-sin²x,同分子約左,
所以得出答案cosx+sinx
2012-05-21 3:23 am
Multiplying (cos x + sin x) to both numerator and denominator can get the ans directly.
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