已知sina/2=12/13,cosa/2=-5/13则a在如题1.已知sin a/2 =12/13(12是分子,13是分母),cos a/2 =-5/13(5是分子,13是分母) 则a在 第几象限?为什么?2.若a是第四象限角,化简根号内1除以(cos a)的平方(只有cosa是平方而
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![已知sina/2=12/13,cosa/2=-5/13则a在如题1.已知sin a/2 =12/13(12是分子,13是分母),cos a/2 =-5/13(5是分子,13是分母) 则a在 第几象限?为什么?2.若a是第四象限角,化简根号内1除以(cos a)的平方(只有cosa是平方而](/uploads/image/z/5427836-44-6.jpg?t=%E5%B7%B2%E7%9F%A5sina%2F2%3D12%2F13%2Ccosa%2F2%3D-5%2F13%E5%88%99a%E5%9C%A8%E5%A6%82%E9%A2%981.%E5%B7%B2%E7%9F%A5sin+a%2F2+%3D12%2F13%2812%E6%98%AF%E5%88%86%E5%AD%90%2C13%E6%98%AF%E5%88%86%E6%AF%8D%29%2Ccos+a%2F2+%3D-5%2F13%285%E6%98%AF%E5%88%86%E5%AD%90%2C13%E6%98%AF%E5%88%86%E6%AF%8D%29+%E5%88%99a%E5%9C%A8+%E7%AC%AC%E5%87%A0%E8%B1%A1%E9%99%90%3F%E4%B8%BA%E4%BB%80%E4%B9%88%3F2.%E8%8B%A5a%E6%98%AF%E7%AC%AC%E5%9B%9B%E8%B1%A1%E9%99%90%E8%A7%92%2C%E5%8C%96%E7%AE%80%E6%A0%B9%E5%8F%B7%E5%86%851%E9%99%A4%E4%BB%A5%28cos+a%29%E7%9A%84%E5%B9%B3%E6%96%B9%28%E5%8F%AA%E6%9C%89cosa%E6%98%AF%E5%B9%B3%E6%96%B9%E8%80%8C)
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