Salut,
[tex]tga+tgb=\dfrac{sina}{cosa}+\dfrac{sinb}{cosb}=\dfrac{sina\cdot cosb+cosa\cdot sinb}{cosa\cdot cosb}=\dfrac{sin(a+b)}{cosa\cdot cosb}.\\\\tg130^{\circ}+tg50^{\circ}=\dfrac{sin(130^{\circ}+50^{\circ})}{cos(130^{\circ})\cdot cos(50^{\circ})}=0.[/tex]
Green eyes.
