−2sin12(2x+5y)sin(2x−5y)-2\sin\frac{1}{2}\left(2x+5y\right)\sin\left(2x-5y\right)−2sin21(2x+5y)sin(2x−5y) jika dituliskan dalam bentuk selisih cosinus menjadi ....
cos5x−cos2y\cos5x-\cos2ycos5x−cos2y
cos2x−cos5y\cos2x-\cos5ycos2x−cos5y
−2(cos2x−cos5y)-2\left(\cos2x-\cos5y\right)−2(cos2x−cos5y)
cos(−2x)−cos5y\cos\left(-2x\right)-\cos5ycos(−2x)−cos5y
cos2x−cos(−5y)\cos2x-\cos\left(-5y\right)cos2x−cos(−5y)