这个求证题怎么做,是关于三角函数的

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这个求证题怎么做,是关于三角函数的
 

(sinα)^2 + (sinβ)^2 - (sinα)^2 * (sinβ)^2 + (cosα)^2 * (cosβ)^2
=[(sinα)^2 - (sinα)^2 * (sinβ)^2] + (sinβ)^2 + (cosα)^2 *(cosβ)^2
=(sinα)^2 * [1 - (sinβ)^2] + (sinβ)^2 + (cosα)^2 *(cosβ)^2
=(sinα)^2 * (cosβ)^2 + (cosα)^2 *(cosβ)^2 + (sinβ)^2
=[(sinα)^2 + (cosα)^2] * (cosβ)^2 + (sinβ)^2
=(cosβ)^2 + (sinβ)^2
=1