17, let an=a 1.
(n- 1)*d,a 1
Aortic second sound
A3= 12 is 3a 1.
3d= 12
D=2, so an=2n and sn = n 2.
ordinary
18, let x 1, x2 belongs to (0,
∞) and x1< x2, f (x1)-f (x2) =1(x12)-1(x2 2) = (x2 2-).
x2^2-x 1^2>; 0, so f(x 1)-f(x2)0.
So this is a subtraction function.
20. let the growth rate be x and the total amount be d.
D*( 1
X)^4=2D
Suppose it takes n years
D*( 1
x)^n=5D
N=0.25 times 2 is the logarithm with base 5.