# Polar coordinates

While locating the polar coordinates of a point, why do we take the initial line as a directed line? Doesn't it suffice to mention that the angle that it makes will be measured with the positive direction of the $x$ axis?
Couldn't we just take a line segment?

• What do you think "a directed line" (?) means? A directed vector is a segment of line with a definite direction, however you define that. Apr 15, 2017 at 9:51
• I never make any mention to directed lines when I look at polar coordinates, I do just say the argument is the angle it makes with the positive $x$-axis. Apr 15, 2017 at 10:31
• @DonAntonio I know what a vector is. It's a directed line segment. But could we do without using a vector while specifying a polar coordinate? Could we not talk of a directed line segment and simply use a line segment? Apr 15, 2017 at 11:02
• @BillWallis Most textbooks start by using the angle made by a directed line segment to define the argument. What I'm asking is couldn't we do without assigning a direction to the initial line segment? We are already saying that the angle is made with the positive direction of the $x$ axis. Apr 15, 2017 at 11:04