Question 16 of 20 Which of the following is the equation of a line perpendicular to the line
y=-3/2x+4, passing through the point (3,9)?
O A. 2x+3y= 21
O B. – 2x – 3y = – 21
O c. – 2x + 3y= 21
O D. 2x – 3y= 21

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) = .