need a little help... i know how to convert given rectangular or polar cordinates.... bu ti have a feeling i should know how to do it with an equation too. help appreciated... might fail here...

instructions on this arent clear, so i need your help.

The letters x and y represent rectangular coordinates. Write in polar cordinates (r, theta)

The letter r and theta represent polar coordinates. Write using rectangular coordinates. (x,y)

a little explanation of the process of this would be much appreciated... im sure it can be very simple.

also does nay one know what the tag for theta is.

thanks, help much appreciated.