решите данное системное уравнение                                                                                     1){x+y=1   x-y=5} ;     2) {2х-7у=39  х+у=-3} ;                                                                                                                                                                                                                                                                                               3) {5х-2у=-12   3х+4у=-2} ;                                                                                                                 4) {х+2у=5    -х+7у=13} решите и сфоткайте!!!Срочно надо!!!!