RQuestion 65-66 thx

65. If f(x) = (x - a)(x - b)(x - c), show that f' (x ) = + f (x) x - a x - b x - C 66. (a) By differentiating the double-angle formula cos 2x = cos2x - sin x obtain the double-angle formula for the sine function. (b) By differentiating the addition formula sin(x + a) = sin x cos a + cos x sin a obtain the addition formula for the cosine function