(3х² - 27)/(18 - 6х) = 3(х² - 9) / 6(3 - х) =
= (х - 3)(х + 3) / (-2)(х - 3) =
= -(х + 3)/2
sin^2A+cos^2A=1, cos2a=cos^2A-sin^2A.
0,3=3/10. 0,3= 6/20 0,3=9/30