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÷a1=?,r=? Daca a1+a3=8,a1+a6=17

Răspuns :

a3=a1+2r
a6=a1+5r
a1+a3=2a1+2r=8 deci a1+r=4 adică a1=4-r
2a1+5r=17 deci 2(4-r)+5r=17
8-2r+5r=17
3r=9
r=3 deci a1=1