两角和与差的三角函数小题,(我只会手写,见谅,
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不用积化和差也行,不过思路是一致的.

分解 x = (x - π/6) + π/6

x-π/3 = (x - π/6) - π/6

所以原式 = cos[(x - π/6) + π/6] + cos[(x - π/6) - π/6] ,利用两角和(差)的余弦公式

= cos(x-π/6)*cos(π/6)- sin(x-π/6)*sin(π/6)+ cos(x-π/6)*cos(π/6)+ sin(x-π/6)*sin(π/6)

= 2*cos(x-π/6)*cos(π/6)

=2*m*(1/2) = m

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