The inclination of a line is the angle θ which the part of the line (above the x-axis) makes with x-axis.
If measured in anti-clockwise direction then the inclination θ is positive and if measured in clockwise direction then the inclination θ is negative.
The inclination of a line or the angle of inclination of the line is the angle which a straight line makes with the positive direction of x-axis measured in the anti-clockwise direction to the part of the line above the x-axis. The inclination is usually denoted by θ.
(i) The inclination of x-axis and every line parallel to x-axis is 0°
i.e. the inclination of a line parallel to x-axis or the x-axis itself is 0°.
(i) The inclination of y-axis and every line parallel to y-axis is 90°
i.e. the inclination of a line parallel to y-axis or the y-axis itself is 90°.