因为sin2A=2sinA·cosA
Cos2a=Cos^2(a)-Sin^2(a)
所以原式=Cos^2(a)+Sin^2(a)+2sinA·cosA-Cos^2(a)+Sin^2(a)除以Cos^2(a)+Sin^2(a)+2sinA·cosA+Cos^2(a)-Sin^2(a)
=2sinA·（sinA+cosA）除以2cosA（sinA+cosA）=tgA
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因为sin2A=2sinA·cosA
Cos2a=Cos^2(a)-Sin^2(a)
所以原式=Cos^2(a)+Sin^2(a)+2sinA·cosA-Cos^2(a)+Sin^2(a)除以Cos^2(a)+Sin^2(a)+2sinA·cosA+Cos^2(a)-Sin^2(a)
=2sinA·（sinA+cosA）除以2cosA（sinA+cosA）=tgA