4) A radioactive isotope is decaying at a rate of 20% every hour. Currently there are 100 grams of the substance.
a) How much is left after 1 hour?

Pranza plotted point a in the coordinate plane below.

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) = .

What unit of been sure would be appropriate for the volume of a sphere with a radius of 2 meters