12. \( \cos \theta\left(1+\tan ^{2} \theta\right) \)
\( \cos \theta\left(\frac{1}{\cos ^{2} \theta}\right) \)
Step 1 :\( \cos \theta\left(1+\tan ^{2} \theta\right) \)
Step 2 :\( \cos \theta\left(1+\frac{\sin ^{2} \theta}{\cos ^{2} \theta}\right) \)
Step 3 :\( \cos \theta\left(\frac{\cos ^{2} \theta + \sin ^{2} \theta}{\cos ^{2} \theta}\right) \)
Step 4 :\( \cos \theta\left(\frac{1}{\cos ^{2} \theta}\right) \)