On a number line, a number, b, is located the same distance from 0 as another number, a, but in the opposite direction. The number b varies directly with the number a. For example b=2 3/4 when a=-2 3/4. Which equation represents this direct variation between a and b?
1) b=-a
2) -b=-a
3) b-a=0
4) b(-a)=0
