令2β = α 左边 =(1+secα+tanα)/(1+secα-tanα) =(cosα + sinα + 1)/(cosα-sinα+1) =(cosα + 1 + sinα)/(cosα+1-sinα) =(cos2β + 1 + sin2β)/(cos2β+1-sin2β) =[2cos^2(β) + 2sinβcosβ]/[2cos^2(...