Ответы и объяснения

2012-01-20T19:48:46+04:00

1)Оценим a+b : 2<a<4

                      +        

                        6<b<11

                     = 8<a+b<15

2)Оценим a+(-b): 2<a<4

                         +

                           -11<a+(-b)<-6

                         =-9<a+(-b)<-2

3)Оценим 1/а+1/b : 1/2 >1/a>1/4

                             +1/6>1/b>1/11

                            =2/3>1/a+1/b>15/44