For help you can see the method of solving these questions at :

http://1nidhi.blogspot.com/2015/07/write-parametric-equation-of-circle.html

http://1nidhi.blogspot.com/2015/07/find-parametric-equation-of-circle.html

http://1nidhi.blogspot.com/2015/07/write-parametric-equation-of-circle.html

http://1nidhi.blogspot.com/2015/07/find-parametric-equation-of-circle.html