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Calculati numarul a= (2+4+6+8+...+4028+4030) * (1/2014*2015 - 1/2015*2016).

Răspuns :

Vezi atas!
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Vezi imaginea CHRISTIAN02
a= (2+4+6+8+...+4028+4030) * [1/(2014*2015) - 1/(2015*2016)]=

=2*(1+2+3+...+2014+2015)* [
1/(2014*2015) - 1/(2015*2016)]=

=2*2015*2016/2*
[1/(2014*2015) - 1/(2015*2016)]=

=2015*2016 *1/ (2014*2015) - 2015*2016*1/ (2015*2016)=

=2016/2014 - 1= 2016/2014-2014/2014= 2/2014= 1/1007