已知cos=-3分之跟号3，为第三象限，求sin，cos，tan
\u5df2\u77e5a\u662f\u7b2c\u4e09\u8c61\u9650\u7684\u89d2\u4e14f\uff08a\uff09sin\uff08a-\u03c0/2\uff09cos\uff083\u03c0/2+a\uff09tan\uff08\u03c0-a\uff09/tan\uff08-a-\u03c0\uff09sin\uff08-a-\u03c0\uff09\u3002\u5316\u7b80\u7b49\u4e8e-cosa
(1)\u5316\u7b80\uff1a\u539f\u5f0f=-cos\u03b1\u00b7sin\u03b1\u00b7(-tan\u03b1)/\uff08-tan\u03b1\uff09
=-cos\u03b1\u00b7sin\u03b1
(2)cos(a-3/2*\u220f)=-sin\u03b1=1/5
\u2234 sin\u03b1=-1/5
\u2235cos²\u03b1+sin²\u03b1=1
\u2234cos\u03b1=\u00b1\uff082\u221a6\uff09/5
\u53c8\u2235\u03b1\u662f\u7b2c\u4e09\u8c61\u9650\u7684\u89d2
\u2234cos\u03b1=-\uff082\u221a6\uff09/5
f\uff08\u03b1\uff09=-cos\u03b1\u00b7sin\u03b1
=-[-\uff082\u221a6\uff09/5]\u00b7\uff08-1/5\uff09
=-\uff082\u221a6\uff09/25
所以sinx=根号（1-cosx^2）
又因为x为第三象限，所以sinx为负值=负的根号(2/3)
tanx=sinx/conx=根号2
cos=-√3/3,
sinα=-√(1-cos^2α)=√[1-(-√3/3)^2].
=-(√6)/3.
tanα=sinα/cosα=(-√6/3)/[-√3/3)].
=√2.
sinα=-√(1-cos^2)=-√6/3,tanα=sinα/cosα=√2
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