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Stiind ca a+b+c=192,b-c=123,2a+b+3c=?

Răspuns :

Spidie
a+b+c=192   +
    b-c=123
__________
a+2b =192+123
a+2b= 315

2a+b+3c= 2a +4b- 3b+3c= 2*(a+2b)-3*(b-c)= 2*315 - 3*123=630-369= 261
Icecon2005
a+b+c=192     
b-c=123
se aduna ambele ecuatii
a+b+c+b-c=192+123
a+2b= 315
2a+b+3c= se desface in :  2a +4b- 3b+3c=

 (a+2b)+(a+2b)-3×(b-c)= 315+315 -3×123=630-369= 261

2a+b+3c=261

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