What is the slope intercept form of - 1/2 and 1, - 1/2 being the slope?

The slope-intercept form of the equation of a straight line is y=mx+b, where m is the slope and b is the y-coordinate of the y-intercept.

If the given slope is - 1/2, then this equation becomes y = (-1/2) x + b.

You do not say that b=1.

But if we let b=1, then the equation becomes y = (-1/2) x + 1.