color(white)(xx)1color(white)(x) "radian"=180/picolor(white)(x)"degrees"×1xradian=180πxdegrees
=>pi/2color(white)(x) "radian"=pi/2*180/picolor(white)(x)"degrees"⇒π2xradian=π2⋅180πxdegrees
color(white)(xxxxxxxxxxx)=90color(white)(x)"degrees"×××××x=90xdegrees