If  O is the origin and the line OP of length r makes an angle α  with x- axis and lies in the xz- plane, then the coordinates of P are

If a P point lines on the xz-plane then the coordinates of the point  P can be taken asx,0,zGiven the angle made by the line with  x-axis is  and the α angle made by the same line with z- axis is  90°−α Therefore, the coordinates of the point Prcosα,0,rsinα