Use the point-slope form of the equation:-
y - y1 = m(x - x1) where m=slope and (x1,y1) is a point on the line
Here we have
y - 5 = -1/2(x - (-5))
y - 5 = -1/2(x + 5)
y = -1/2x - 5/2 + 5
y = -1/2x + 5/2
this can also be written as
2y = -x + 5
or in standard form it is x + 2y = 5
