\f(Except for notation, this is the equation of Exercise 71.) (b) Show that o can be written in the form 9(1) = A sino + Bcos at where A, B, w are constants. 73. An isosceles triangle has two sides of length c. The angle between them is x radians. Express the area A of the trian- gle as a function of x and find the rate of change of A with respect to r. 74. A triangle has sides of length a and b, and the angle between them is x radians. Given that a and b are kept constant, find the rate of change of the third side c with respect to x. HINT: Use the law of cosines