PLS HELP TIMED Which expressions are equivalent to 4(9+3)?

a
4(12)
b
36 + 3
c
36 + 12
d
4 + (9 + 3)
e
(9 + 3) + (9 + 3) + (9 + 3) + (9 + 3)

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) = .