$\sin a\cos b+\cos a\sin b$  

 $\sin a\cos b-\cos a\sin b$  

 $\cos a\cos b+\sin a\sin b$  

 $\cos a\cos b-\sin a\sin b$  

 $u\left(x\right)=-\frac{\pi}{2}+k\pi,k\in Z$  

 $u\left(x\right)=\frac{\pi}{2}+k2\pi,k\in Z$  

 $u\left(x\right)=-\frac{\pi}{2}+k2\pi,k\in Z$  

 $u\left(x\right)=k\pi,k\in Z$  

 $u\left(x\right)=v\left(x\right)+k2\pi,\ u\left(x\right)=-v\left(x\right)+k2\pi,\ k\in Z$  

 $u\left(x\right)=v\left(x\right)+k2\pi,\ u\left(x\right)=\pi-v\left(x\right)+k2\pi,\ k\in Z$  

 $u\left(x\right)=v\left(x\right)+k2\pi,k\in Z$  

 $u\left(x\right)=v\left(x\right)+k\pi,\ u\left(x\right)=-v\left(x\right)+k\pi,\ k\in Z$  

 $-\cos u=\cos\left(-u\right)$  

 $-\cos u=\cos\left(\frac{\pi}{2}-u\right)$  

 $-\cos u=\cos\left(\pi-u\right)$  

 $-\cos u=\sin\left(\frac{\pi}{2}-u\right)$  

 $-\sin u=\sin\left(-u\right)$  

 $-\sin u=\sin\left(\frac{\pi}{2}-u\right)$  

 $-\sin u=\sin\left(\pi-u\right)$  

 $-\sin u=\cos\left(\frac{\pi}{2}-u\right)$  

 $-2\cos4x\sin x$  

 $-2\sin4x\sin x$  

 $2\sin4x\sin x$  

 $2\cos4x\cos x$  

 $\cos4x+\cos2x$  

 $\cos4x-\cos2x$  

 $\cos4x+\sin2x$  

 $\cos4x-\sin2x$  

$1+\tan^2x=\frac{1}{\sin^2x}$

$\sin3x=3\sin x\cos x$

$\cos4x=2\cos^22x-1$

$\cos\left(\alpha+\frac{\pi}{2}\right)=\sin\alpha$

$1+\cos2a=2\cos^2a$

$5\sin x-3=0$

$3\sin x-5=0$

$\sin3x=3$

$\sqrt{7}\sin x-\sqrt{10}\cos x=\sqrt{15}$

$\sin x+2\cos x=3$