20 Letf(x) = 6cos( 3 36+ 8571). (a) What is the range of f? (b) What is the amplitude of f? (c) What is the period of f? (d) By what fraction of the period of 6 cos( 3x x) should the graph of 6 cos( 3x x) be shifted left to obtain the graph of f? (e) Sketch the graph of f on the interval [9, 9]. (f) Sketch the graph of 6 cos( 3 x + 85 ) + 7 on the 1n- terval [ 9, 9]