If θ be the angle at which a straight line is inclined to the positive direction of x-axis, the slope of the line is defined by m=tanθ where 0∘≤θ<180∘ θ≠90∘
1. when θ=0∘
Slope =tanθ=tan0∘=0
2. when θ=90∘
at θ = 90∘ slope of the line is NOT defined
3. when θ=120∘
Slope of line =tan120∘=tan(180∘−60∘)=−tan60∘=−√3
4. when θ=150∘
Slope of line =tan150∘=tan(180∘−30∘)=−tan30o=−1√3