1) cos x = 1/2 2) cos 2*x = -1
F(-2)= 4+10-6=4
12x(x+3)+5x(x-3)-18(x²- 9)=0
12x²+36x+5x²-15x-18x²+162=
-x²+21x+162=0
x²-21x-162=0
D=441+648=1048
х₁= (21+33)/2=27
х₂= (21-33)/2= -6