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20060521jr
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calculeaza 1+2+3+...+50+(-1)+(-2)+(-3)+...+(-55) repede pls​

Răspuns :

Radusss

1+2+3+...+50+(-1)+(-2)+(-3)+...+(-55) = (1-1) + (2-2) + ... + (50-50) -51-52-53-54-55 =  

= -265

Loredanaschneid

1+2+3+...+50+(-1)+(-2)+(-3)+...(-55)=

= 1+2+...+50-1-2-...-55=

=1+2+...+50-(1+2+...+55)=

[tex] = \frac{50 \times 51}{2} - \frac{55 \times 56}{2} = [/tex]

= 25x51-55x28=

=1275-1540=

= -265

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