Find the period and the amplitude. y = cos (8x/17) STEP 1: Rewrite the trigonometric expression in the form y = a cos (bx). y = cos (8x/17) = - cos ((8/17) STEP 2: Find the period of y by dividing 2 by b. x) 17π 4 Does this period represent a horizontal stretching of the graph of y = a cos (x) or a horizontal shrinking of the graph of y = a cos (x)? horizontal stretching horizontal shrinking STEP 3: Will the amplitude of y be positive or negative? Positive, because both 8 and 17 are positive. Positive, because the leading coefficient of y is negative. Negative, because both 8 and 17 are positive. Positive, because amplitude measures a distance. Negative, because the leading coefficient of y is negative. Find the amplitude of y. 1