\(a,VT=\left(\sin^252^0+\sin^238^0\right)-\left(\tan37^0-\cot53^0\right)+\dfrac{\tan42^0}{\tan42^0}\\ =\left(\sin^252^0+\cos^252^0\right)-\left(\tan37^0-\tan37^0\right)+1\\ =1-0+1=2=VP\\ c,VT=\dfrac{2\cos^2\alpha-\sin^2\alpha-\cos^2\alpha}{\sin\alpha+\cos\alpha}=\dfrac{\cos^2\alpha-\sin^2\alpha}{\sin\alpha+\cos\alpha}\\ =\dfrac{\left(\cos\alpha-\sin\alpha\right)\left(\cos\alpha+\sin\alpha\right)}{\cos\alpha+\sin\alpha}=\cos\alpha-\sin\alpha=VP\\ b,VT=\cos^2\alpha+\cos^2\alpha\cdot\dfrac{\sin^2\alpha}{\cos^2\alpha}=\cos^2\alpha+\sin^2\alpha=1=VP\)
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