∴(a3+a6)-(a2+a5)

=a3+a6-a2-a5

=2d

=-30-(-22)

=-8

That is, d=-4.

Then a2+a5 = 2a1+5d = 2a1-20 =-22.

Solution: a 1=- 1

The general formula of the sequence an is:

an=a 1+(n- 1)d

=- 1+(n- 1)*(-4)

=-4n+3

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