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80 .   If   cot   θ = 12 5 ,   show   that   tan 2   θ - sin 2   θ = sin 4   θ   sec 2   θ .

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Given: cotθ=125=BPBy pythagoras theorem, we haveH2=P2+B2    , where P=Perpendicular,B=base,H=hypotenuse.H2=52+122H2=25+144H2=169H=13 units.Now, tanθ=PB=512sinθ=PH=513secθ=HB=1312Consider LHStan2θ-sin2θ=5122-5132=25144-25169=4225-360024336=62524336  ...1Consider RHSsin4θ sec2θ=5134×13122=625169×144=62524336  ...2From 1 and 2RHS=LHSHence Proved
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