CAB5910[Graphs generated by this script: initPicture(-1,10,-10,1);line([0,0],[0,-9]);line([0,0],[5,0]);line([5,0],[0,-9]);line([0.6,0],[0.6,-0.6]);line([0,-0.6],[0.6,-0.6]);text([-0.5,0.5],"C");text([0,-9.9],"A");text([5.9,0],"B");text([5.9/2,0.5],"5");text([-0.5,-9.9/2],"9");text([5.9/2,-9.9/2],"10")]

Note: Triangle is not to scale.

In right triangle ABC above, what is the cosine of B?