Question 1058388
*[illustration sine.png]
<pre><b>
I must redraw the figure,with a vertical line drawn from (8,6)
down to the x-axis, forming a right triangle:

{{{drawing(150,2650/21,-2.3,10.3,-2.3,8.3,line(8,6,8,0),
locate(2.5,1.5,theta), locate(8.2,3.2,6), locate(4,3,a),locate(8,6,"(8,6)"),
graph(150,2650/21,-2.3,10.3,-2.3,8.3), line(0,0,8,6),circle(8,6,.2) )}}}

We calculate hypotenuse "a" by the Pythagorean theorem:

{{{a^2}}}{{{""=""}}}{{{6^2+8^2}}}
{{{a^2}}}{{{""=""}}}{{{36+64}}}
{{{a^2}}}{{{""=""}}}{{{100}}}
{{{a}}}{{{""=""}}}{{{sqrt(100)}}}
{{{a}}}{{{""=""}}}{{{10}}}

{{{cos(theta)}}}{{{""=""}}}{{{adjacent/hypotenuse}}}{{{""=""}}}{{{8/10}}}{{{""=""}}}{{{4/5}}}

Choice D.)

Edwin</pre>