數學問題一問..(thx)萬分感激!!!!!

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1.1-sin^2x=cos^2x(因為cos^2x+sin^2x=1)
1-sin^2x/cosx
=cos^2x/cosx
=cosx

2.tan^2x=sin^2x/cos^2x
tan^2x+2
=(sin^2x/cos^2x)+2
=(2sin^2x/cos^2x)+(2cos^2x/cos^2x)............[[通份母]]
=(2sin^2x + 2cos^2x)/cos^2x
=2(sin^2x+cos^2x)/cos^2x...........[[抽2]]
=2/cos^2x................[[sin^2x+cos^2x=1]]

3.(1-sinx)2(1+sinx)..............[[抽2]]即係2乘(1-sinx)乘(1+sinx)
=2(1-sinx)(1+sinx)
=2(1^2 - sin^2x)........[[(a+b)(a-b)=a^2 - b^2]]
=2(1-sin^2x)
=2cos^2x

4.(1-cos^2x)/(1-sin^2x)
=sin^2x/cos^2x
=tan^2x

5.(sin^2x+sin^2x)/tan^2x
=(2sin^2x)/(sin^2x/cos^2x)
=(2sin^2x)(cos^2x/sin^2x).....[[a/(b/c)=a(c/b)(除b/c會變做乘c/b]]
=2cos^2x.....[[約左sin^2x]]