a) sin2atan2a+4sin2a−tan2a+3cos2a=(sin2atan2a+sin2a)−tan2a+3(sin2a+cos2a)=sin2a(tan2a+1)−tan2a+3=sin2a.1cos2a−tan2a+3=tan2a−tan2a+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)
=sin2a(tan2a+1)−tan2a+3=\sin^{2}a.\dfrac{1}{\cos^{2}a}-\tan^{2}a+3=\tan^{2}a-\tan^{2}a+3=3$