cos^2 75°+cos^2 15°+cos75°+cos15°,

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cos^275°+cos^215°+cos75°+cos15°,cos^275°+cos^215°+cos75°+cos15°,cos^275°+cos^215°+cos75°+cos15°,cos^

cos^2 75°+cos^2 15°+cos75°+cos15°,
cos^2 75°+cos^2 15°+cos75°+cos15°,

cos^2 75°+cos^2 15°+cos75°+cos15°,
cos^2 75°+cos^2 15°+cos 75°+cos 15°
=cos^2 75°+Sin^2 75°+cos 75°+Sin 75°
=1+cos 75°+Sin 75°
=1+(√2)(√2/2cos 75°+√2/2Sin 75°)
=1+√2(Cos 45°Cos 75°+Sin 45°Sin 75°)
=1+√2Cos (45°-75°)
=1+√2Cos 30°
=1+√2*√3/2
=1+√6/2