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28+29+30+.......+43​

Răspuns :

28+29+30+...+43=

=1+2+3+...+27+28+29+30+...+43 - (1+2+3+...+27)=

=43×(43+1):2-27×(27+1):2=

=43×44:2-27×28:2=

=43×22-27×14=

=946-378=

=568

Explicație pas cu pas:

28+29+30+...+43=(27+1)+(27+2)+(27+3)+...+(27+16)=

=27*16+8*17=568

Bafta!