S = V ( P * ( P - A)*(P - B)*(P - C) ) P = 0.5*( A + B + C) = 0.5 * ( 11 + 5 + 7) = 0.5 * 23 = 11.5 S = V ( 11.5 * ( 11.5 - 11)*(11.5 - 5)*(11.5 - 7) ) = = V ( 11.5 * 0.5 * 6.5 * 4.5) = V 168.1875 = 12.93 (округляем до 13 ) Ответ 13