已知cos2x=4/5,且x屬于(7派/4,2派),求值:(1)(sin^4)x+(cos^4)x;(2)tan(x/2)
已知cos2x=4/5,且x屬于(7派/4,2派),求值:(1)(sin^4)x+(cos^4)x;(2)tan(x/2)
數(shù)學(xué)人氣：139 ℃時(shí)間：2020-05-21 07:41:21
優(yōu)質(zhì)解答
(1)利用同角三角函數(shù)關(guān)系是sin^2x+cos^2x=1而cos2x=cos^2x-sin^2x=4/5聯(lián)立方程,解得：sin^2x=1/10,cos^2x=9/10;所以(sin^4)x+(cos^4)x=(1/10)^2+(9/10)^2=41/50(2)由于x屬于（7π/4,2π）且由（1）有sinx= - 根號(hào)10/...
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