角a是锐角,cos(a-π/4)=4/5那么sina=多少cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 == 4/5 x √2/2 + 3/5 x √2/2这步为什么?
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![角a是锐角,cos(a-π/4)=4/5那么sina=多少cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 == 4/5 x √2/2 + 3/5 x √2/2这步为什么?](/uploads/image/z/7173584-8-4.jpg?t=%E8%A7%92a%E6%98%AF%E9%94%90%E8%A7%92%2Ccos%EF%BC%88a-%CF%80%2F4%29%3D4%2F5%E9%82%A3%E4%B9%88sina%3D%E5%A4%9A%E5%B0%91cos%28a+-+%CF%80%2F4%29cos%CF%80%2F4+%2B+sin%28a+-+%CF%80%2F4%29sin%CF%80%2F4+%3D%3D+4%2F5+x+%E2%88%9A2%2F2+%2B+3%2F5+x+%E2%88%9A2%2F2%E8%BF%99%E6%AD%A5%E4%B8%BA%E4%BB%80%E4%B9%88%EF%BC%9F)
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角a是锐角,cos(a-π/4)=4/5那么sina=多少cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 == 4/5 x √2/2 + 3/5 x √2/2这步为什么?
角a是锐角,cos(a-π/4)=4/5那么sina=多少
cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 =
= 4/5 x √2/2 + 3/5 x √2/2
这步为什么?
角a是锐角,cos(a-π/4)=4/5那么sina=多少cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 == 4/5 x √2/2 + 3/5 x √2/2这步为什么?
sina =cos(π/2 - a) = cos(a - π/2) = cos( a - π/4 - π/4)
= cos(a - π/4)cosπ/4 + sin(a - π/4)sinπ/4 =
= 4/5 x √2/2 + 3/5 x √2/2 = 7/5 x √2/2 = 7√2/10
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