http://www.google.co.in/imgres?q=straight+angle&hl=en&client=firefox-a&rls=org.mozilla:en-US:official&gbv=2&biw=1360&bih=583&tbm=isch&tbnid=ct682_NI6ejVpM:&imgrefurl=http://www.mathsisfun.com/geometry/straight-angle.html&docid=KQ1ud6TaBIvmKM&imgurl=http://www.mathsisfun.com/geometry/images/straight-angle.gif&w=277&h=102&ei=FGz1TsqwMYP5rQfRsqjbDw&zoom=1&iact=hc&vpx=656&vpy=254&dur=1422&hovh=81&hovw=221&tx=107&ty=45&sig=101892148739726518788&page=1&tbnh=81&tbnw=219&start=0&ndsp=10&ved=1t:429,r:2,s:0