13- 0.75w + 8x when w = 12 and x = 1/2

Twelve friends shared 8 small pizzas equally. how many pizzas did each person get?

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

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) = .