已知等差数列{an}中,若a1+a6=-17,a2*a5=52,且d>0,求a5和an

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已知等差数列{an}中,若a1+a6=-17,a2*a5=52,且d>0,求a5和an
已知等差数列{an}中,若a1+a6=-17,a2*a5=52,且d>0,求a5和an

已知等差数列{an}中,若a1+a6=-17,a2*a5=52,且d>0,求a5和an
a1+a6=-17
a1+(a1+5d)=-17
(a1+d)+(a1+4d)=-17
a2+a5=-17
a2×a5=52
因为d>0,所以a5>a2
由上面方程可解得
a2=-13,a5=-4
a5=a2+3d
-4=-13+3d
3d=9
d=3
an=a1+(n-1)d
=a2+(n-2)d
=-13+3(n-2)
=3n-19