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Scoate factor comun : 25+50+75+100+..... +400

Răspuns :

=25×1+25×2+25×3+...+25×16=
=25(1+2+3+...+16)

Daca vrei si rezolvarea....
=25(16×17:2)=
=25×8×17=
=200×17=
=3400
25+50+75+100+..... +400 = 
25 ( 1 +2 + 3 +4 +.....+ 16) = 
25 x 16 x 17 : 2 = 3400