sin平方π/3=3/4 过程 为什么》？？？
sin3/4\u03c0\u4e3a\u4ec0\u4e48\u7b49\u4e8esin(\u03c0-3/4\u03c0)??\u8fd9\u662f\u4ec0\u4e48\u516c\u5f0f\u5417?\u7b54\uff1a
\u4e09\u89d2\u51fd\u6570\u7684\u8bf1\u5bfc\u516c\u5f0f\uff1asin(\u03c0-a)=sina
sin^2 \u03c0/3+cos^4 3\u03c0/2-tan^2 \u03c0/3
=3/4+0-3
=-9/4
\u5982\u679c\u5e2e\u5230\u60a8\u7684\u8bdd\uff0c\u53ef\u4ee5\u597d\u8bc4\u5417\uff1f\u8c22\u8c22\u4e86\uff01\uff01\uff01(\u53f3\u4e0a\u89d2\u91c7\u7eb3)
所以sin²（π/3）=（√3/2）²=3/4
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