請高手幫忙啊 若α∈(0，π/2),a?b?o,求f(α)=a^2/(cosα)^2+b^2/(sinα)^2的最小值要過程啊

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若α∈(0，π/2),a?b?o,求f(α)=a^2/(cosα)^2+b^2/(sinα)^2的最小值f(α)=a^2/(cosα)^2+b^2/(sinα)^2=a^2*[1+(tanα)^2]+b^2*[1+(cotα)^2]=a^2 +b^2 + (a*tanα)^2 + (b*cotα)^2≥a^2+b^2 + 2ab (均值不等式）所以(tanα)^2=b/a 時，f(α)的最小值為：(a+b)^2