(c) Select the graph with the shape that best fits the summary values. Graph 1 (The data set is symmetric.)
Graph 2 (The data set is not symmetric.)
Number of days
Number of days
72 73 74 75 76 77 78
Temperature (°F)
79 80
72 73 74 75 76 77 78
Temperature (°F)
79 80

Prove (a) cosh2(x) − sinh2(x) = 1 and (b) 1 − tanh 2(x) = sech 2(x). solution (a) cosh2(x) − sinh2(x) = ex + e−x 2 2 − 2 = e2x + 2 + e−2x 4 − = 4 = . (b) we start with the identity proved in part (a): cosh2(x) − sinh2(x) = 1. if we divide both sides by cosh2(x), we get 1 − sinh2(x) cosh2(x) = 1 or 1 − tanh 2(x) = .