A=cos7x−cos9x+cos10x−cos8xsin7x−sin9x+sin10x−sin8x=2sin8x.sinx−2sin9x.sinx−2cos8x.sinx+2cos9x.sinx=2sinx(sin8x−sin9x)2sinx(cos9x−cos8x)=sin8x−sin9xcos9x−cos8x$=\frac{2cos\frac{17x}{2}.sin\frac{x}{2}}{-2sin\frac{17x}{2}.sin\frac{x}{2}}=-tan\frac{17x}{2}$
A=cos7x−cos9x+cos10x−cos8xsin7x−sin9x+sin10x−sin8x=2sin8x.sinx−2sin9x.sinx−2cos8x.sinx+2cos9x.sinx=2sinx(sin8x−sin9x)2sinx(cos9x−cos8x)=sin8x−sin9xcos9x−cos8x$=\frac{
-2cos\frac{17x}{2}.sin\frac{x}{2}}{-2sin\frac{17x}{2}.sin\frac{x}{2}}=tan\frac{17x}{2}$