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cat fac 2+4+6+....+88 dau coroana


Răspuns :


2+4+6+00000+88=2x(1+2+3+....+44)=

                              2x(44x(44+1):2)=

                              2x( 44x45:2)=

                               2x(1980:2)=1980

                                   2x990=1980

                           

=2(1+2+3+...+44)=2(44•45:2)=44•45=1980