impedance UZ

https://www.wikiskripta.eu/w/Ultrazvuk_v_r%C5%AFzn%C3%BDch_prost%C5%99ed%C3%ADch_a_tk%C3%A1n%C3%ADch#Ultrazvuk_na_tk.C3.A1.C5.88ov.C3.A9m_rozhran.C3.ADv

k ... kost
t ... tkáň

Z_k, Z_t
Z_k = n.Z_t
n = ?
---------------------

R = 36% = 0,36

R = [(Z_k - Z_t)/(Z_k + Z_t)]^2
R = [(n.Z_t - Z_t)/(n.Z_t + Z_t)]^2
R = [(n-1)/(n+1)]^2
R.(n+1)^2 - (n-1)^2 = 0
Rn^2 + 2Rn + R - n^2 + 2n - 1 = 0
(R-1).n^2 + 2(R+1)n + (R-1) = 0
-0,64.n^2 + 2,72.n - 0,64 = 0

n1 = 4
n2 = 1/4

https://www.wolframalpha.com/input/?i=solve+-0.64n%5E2+%2B+2.72n+-+0.64+%3D+0

Výpočet z hlavy:

-0,64.n^2 + 2,72.n - 0,64 = 0
krát -100
64n^2 - 272n + 64 = 0
děleno 16
4n^2 - 17n + 4 = 0

D = 289-4.4.4 = 225 = 15^2

n1,2 = (17 +/- 15)/8

n1 = 4
n2 = 1/4