Note that this is a right triangle, and that the length of the hypotenuse (17) is given, as is one of the acute angles (30 degrees). We need to determine the length of the "adjacent side," that is, the side of the triangle adjacent to the 30 degree angle. Which of the 6 trig functions relates the 30 degree angle, the length of the hypo. and the length of the adj. side?
cos theta = (adjacent side) / (hypotenuse)
Then cos 30 degrees = x / 17 units, or (17 units) cos (30 degrees) = x
Use your calculator to find the value of cos 30. Multiply your result by (17 units).
The result is your answer (the length of the horiz. side, DF).
