Question

в арифмеиической прогрессии a3 = 7 и a5 = 1. Найдите a17

Answer 1

a3=7,a5=1,a17=?

an=a1+(n-1)d

a17=a1+16d

a5-a3=2d, 2d=1-7=-6, d=-3

a1=a3-2d, a1=7-2(-3)=7+6, a1=13

a17=13+16(-3)=13-48

a17=-35

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