John needs to paint a wall with spray paint. the wall has a diagonal of 43.6 feet and a height of 8.3 feet. if a spray can will cover 21.5 square feet, how many cans will john need? (round to nearest whole number) a) 12 cans b) 14 cans c) 16 cans d) 17 cans

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) = .