a; \(A=3\cdot cos\left(\pi-x\right)-5\cdot cos\left(\frac52\pi-x\right)+\cot\left(4\pi-x\right)+\tan\left(\frac72\pi-x\right)\)
\(=-3\cdot cosx-5\cdot cos\left(2\pi+\frac{\pi}{2}-x\right)+\cot\left(-x\right)+\tan\left(\frac{\pi}{2}-x\right)\)
\(=-3\cdot cosx-5\cdot cos\left(\frac{\pi}{2}-x\right)-\cot x+\cot x\)
\(=-3\cdot cosx-5\cdot\sin x\)
b: \(B=cos\left(270^0-x\right)-2\cdot\sin\left(x-450^0\right)+cos\left(x+900^0\right)+2\cdot\sin\left(-x\right)+cos\left(540^0-x\right)\)
\(=cos\left(360^0-90^0-x\right)-2\cdot\sin\left(x-90^0-360^0\right)+cos\left(x+180^0+720^0\right)-2\cdot\sin x+cos\left(360^0+180^0-x\right)\)
\(=cos\left(-90^0-x\right)-2\cdot\sin\left(x-90^0\right)+cos\left(x+180^0\right)-2\cdot\sin x+cos\left(180^0-x\right)\)
\(=cos\left(x+90^0\right)+2\cdot\sin\left(90^0-x\right)-cosx-2\cdot\sin x-cosx\)
=-sin x+2*cosx-2*cosx-2*sin x
=-3*sin x
