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...