По теореме косинусов:
AC^2 = AB^2 + BC^2 - 2*AB*BC*cos<ABC.
16 = 4+9-2*2*3*cos<ABC;
16=13-12cos<ABC; 12cos<ABC=13-16; cos<ABC= -3/12 = -1/4.
По теореме косинусов:
AC^2 = AB^2 + BC^2 - 2*AB*BC*cos<ABC.
16 = 4+9-2*2*3*cos<ABC;
16=13-12cos<ABC; 12cos<ABC=13-16; cos<ABC= -3/12 = -1/4.