数列an中an=32sn=63,①若数列an为公差为1的等差数列,求a1②若数列an首相...

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数列an中an=32sn=63,①若数列an为公差为1的等差数列,求a1②若数列an首相...
数列an中an=32sn=63,①若数列an为公差为1的等差数列,求a1②若数列an首相为a1=1,求数列an平方的前n项和Tn

sn=n(a1+an)/2
63=n(a1+32)/2①
sn=n*a1+n*(n-1)*d/2
63=n*a1+n*(n-1)/2②
解①②式得
a1=-28
n=31