Question 309300
If you draw the triangle and label it's parts, you'll see that triangle ABC is a right triangle. Now let's use angle BCA=75 degrees as our reference angle. The side BC is the adjacent side while the side AB is the opposite side (again, a drawing will help). So we're going to use the tangent function (since tan=opposite/adjacent)



So this means that tan(75)=BC/AB and that tan(75)=20/x where 'x' is the length of AB. Now compute tan(75) to get approximately 3.73205. So 3.73205=20/x



Now you're job is to solve the equation 3.73205=20/x to find 'x' which is the length of AB.



Note: There is a way to compute the tangent of 75 degrees exactly, but we don't need to do that here.