12:18=x:(x+4)
12(x+4)=18x
6x=48
x=[b]8[/b]
x+4=[b]12[/b]
Третья сторона 8+12
P=12+18+(8+12)=...
8.
(sqrt(3))^2-x^2=[b]h^2[/b]
(sqrt(6))^2-(3-x)^2=[b]h^2[/b]
Приравниваем:
(sqrt(3))^2-x^2=(sqrt(6))^2-(3-x)^2
3-x^2=6-(3-x)^2
3-x^2=6-9+6x-x^2
6x=6
x=[b]1[/b]
3-x=3-1=[b]2[/b]
8.
AD^2=AB^2+BD^2-2AB*BD*cos ∠ B
cos ∠ B=(8^2+4^2-10^2)/2*8*4=-5/16
AC^2=AB^2+BC^2-2AB*BC*cos ∠ B=8^2+16^2-2*8*16*(-5/16)=400
AC=2