A)
19*18!-18*18! - (17*17!)/(18*17!-17!)=1-(17*17!)/(17!*17)=1-1=0
б)
(9!+10!+11!)/(12*11!-11!)=(9!+10*9!+110*9!)/(12*110*9!-110*9!)=(1+10+110)/(11*110)=121/(11*11*10)=0.1
t =√(2h/a)
t²= 2h/a
2h=t²*a
h= t²*a/ 2
<span>9^(6+х)=81^2х
3^(12+2x)=3^8x
12+2x=8x
8x-2x=12
6x=12
x=2</span>