Question

rezolvati ecuatia: -5-3-1+1+....+x=72

Answer 1

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Sn=(a1+an)*n/2   
Sn=(a1+a1+(n-1)*n/2   r=2
Sn=(-5+(-5)+(n-1)*r)*n/2=72
(-10+(n-1)*2)*n=144
(-10+2n-2)*n=144
(-12+2n)*n=144
2n²-12n-144=0
n2-6n-72=0
n1=-6∉N
n2=12
x=(12-1)*2=11*2=22