straight lines

Slope of a straight line = tan θ.

If we select any of the two lines as with slope 1/2 making an angle θ with x axis, then the other line can be,

tan (θ±π/4).

Then the slope of the other line = tan (θ±π/4) = (tanθ±tanπ/4)/(1 - or + tanπ/4 tanθ),

is (1/2 - 1)/(1+1/2) = -1/3 or (1/2 + 1)/(1-1/2) = 3.

Regards,

Team,

TopperLearning.