sin(π/10)cos(π/5)
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sin(π/10)cos(π/5)
sin(π/10)cos(π/5)
sin(π/10)cos(π/5)
原式=2sin(π/10)cos(π/10)cos(π/5)/2cos(π/10)
=sin(π/5)cos(π/5)/2cos(π/10)
=2sin(π/5)cos(π/5)/4cos(π/10)
=sin(2π/5)/4cos(π/10)
=cos(π/2-2π/5)/4cos(π/10)
=cos(π/10)/4cos(π/10)
=1/4
分子分母同乘以4cos(π/10),接下来就好做了
没有什么简便的,就是利用乘法分配律乘出来
18:32=9:16
0.25:1.8=5:14
1.2:3/4=8:5
11/12 :22/9=3:8
CaB={-1}
分子分母同乘以一个不等于0的数,分数值不变
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