a) $\sin^{2}a\tan^{2}a+4\sin^{2}a-\tan^{2}a+3\cos ^{2}a=(\sin^{2}a\tan^{2}a+\sin^{2}a)-\tan^{2}a+3(\sin^{2}a+\cos^{2}a)$$=\sin^{2}a(\tan^{2}a+1)-\tan^{2}a+3$$=\sin^{2}a.\dfrac{1}{\cos^{2}a}-\tan^{2}a+3=\tan^{2}a-\tan^{2}a+3=3$
a) $\sin^{2}a\tan^{2}a+4\sin^{2}a-\tan^{2}a+3\cos ^{2}a
$$=(\sin^{2}a\tan^{2}a+\sin^{2}a)-\tan^{2}a+3(\sin^{2}a+\cos^{2}a)$$=\sin^{2}a(\tan^{2}a+1)-\tan^{2}a+3$$=\sin^{2}a.\dfrac{1}{\cos^{2}a}-\tan^{2}a+3=\tan^{2}a-\tan^{2}a+3=3$