Two rays with one common end point.

Right anglenghttp://img705.imageshack.us/i705/3530/20110628165420.p

http://i.imgur.com/Afgy6.png

https://lilrave420.files.wordpress.com/2011/05/2011-05-05_01-45-191.png

Measures exactly 90 degrees.

An angle that is smaller than a right angle.

http://media.showme.com/files/684429/pictures/thumbs/1623111/last_thumb1408905477_200x150.jpg

http://img.wonderhowto.com/img/72/42/63475372343769/0/use-protractor-measure-height-any-object.1280x600.jpg

ACUTE

Bigger than a right angle and so, it is more than 90 degrees

http://www.wqsb.qc.ca/philemon/pmessier/images/obtuse_angle.gif

http://img.wonderhowto.com/img/79/41/63456304387342/0/create-parabolic-curves-using-straight-lines.w654.jpg

http://static.planetminecraft.com/files/resource_media/screenshot/1410/2014-03-07_091507.jpg