<p>for number 17, we know that l represents the total side and the hypotenuse of the other triangle. Hence, l-lcos(theta) =h. then for 18 just plug in the values that they present in the question. For 5 the two right traingles are similar. Thus theta5 and theta 2 are 55. Then do 180= 70+2(theta1), and solve for theta one. Since you have theta 1 you can easily solve for the other two angles presented. Hope this helps!</p>