Zgjidhja e ushtrimit 11

Vërtetoni identitetet e mëposhtme.

1. $\frac{sin(\alpha + \beta)}{cos\alpha cos\beta}$ $\equiv$ tg$\alpha$ + tg$\beta$
2. cotg$\alpha$ $\equiv$ $\frac{sin2\alpha + cos\alpha}{1+sin\alpha - cos2\alpha}$
3. $\frac{sin2\alpha}{1-cos2\alpha}$ $\equiv$ cotg$\alpha$
4. $\frac{sin2\alpha + sin\alpha}{cos2\alpha + cos\alpha + 1}$ $\equiv$ tg$\alpha$