Andy C. answered • 11/01/17

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y = Mx + b where M<0 and b>0

For x<0, Mx > 0 , which means Mx+b > 0.

So when x<0 y > 0 which lies in quadrant 2.

For x=0, y=b > 0 which is the positive y axis in between quadrants 1 and 2.

for x > 0, Mx < 0.

So Mx + b can be either positive or negative depending on x.

That means the line is in either quadrants 1 or 4.

**SUPPOSE**the line is in quadrant 3, where x and y are both negative.

Then x<0 and y < 0.

Mx > 0 <--- negative times negative is positive.

since b>0, y = Mx +b > 0.

which contradicts the assumption that y<0.

So the line

**CANNOT**be in quadrant 3.Therefore the line passes through quadrants 1,2,and 4