Find perpendicular distance from the origin of the line joining the points `(costheta,sintheta)`and `(cosvarphi,sinvarphi)`.

Explanation

equation of line passing through the points `(cos theta, sin theta)` and `(cos phi, sin phi)` is
`y-sintheta=(sinphi-sintheta)/(cos phi- cos theta)(x-cos theta)`
`=(2cos"((phi+theta)/(2))sin((phi-theta)/(2)))/(-2sin((phi+theta)/(2))sin((phi-theta)/(2)))(x-cos theta)`
`=-(cos((theta+phi)/(2)))/(sin((phi+theta)/(2)))(x-costheta)`
`implies y sin((phi+theta)/(2))-sintheta sin((phi+theta)/(2))`
`=-x cos((theta+phi)/(2))+costhetacos((theta+phi)/(2))`
`xcos((theta+phi)/(2))+y sin ((theta+phi)/(2))-costhetacos((theta+phi)/(2))+sin theta sin ((theta+phi)/(2))=0`
`implies xcos "(theta+phi)/(2)+y sin"(theta+phi)/(2)-cos(theta-(theta+phi)/(2))=0`
`implies x cos"(theta+phi)/(2)+y sin"(theta+phi)/(2)-cos((theta-phi)/(2))=0`
Length of perpendicular form origin i.e., `(0,0)` to this line
`=|(0+0-cos((theta-phi)/(2)))/(sqrt(cos^(2)((theta+phi)/(2))+sin^(2)((theta+phi)/(2))))|`
`=|cos"(theta-phi)/(2)|`