When you know the slope [tex]m[/tex] and a point [tex](x_0,y_0)[/tex] of a line, the equation of the line is given by
[tex]y-y_0=m(x-x_0)[/tex]
So, your line is given by
[tex]y-2=-\dfrac{1}{2}(x+1) \iff y=-\dfrac{1}{2}x-\dfrac{1}{2}+2=-\dfrac{1}{2}x+\dfrac{3}{2}[/tex]
