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a15=-25, a32=-42
(1)d=a32=a15+17d
-42=-25+17d
-17=17d
d=-1
(2)a25=a15+10d
=25+10*-1
=-25-10=-35
1.圈問項:(1)公差 (2)a25
2.key-point: an=a1+(n-1)d
3.代數字:
(1)d=a32=a15+17d,-17=17d,d=-1
(2)a25=a15+10d,-25+10*-1=-35
4.寫答: A:-35
(1)d=a32=a15+17d
-42=-25+17d
-17=17d
d=-1
(2)a25=a15+10d
=25+10*-1
=-25-10=-35
1.圈問項:(1)公差 (2)a25
2.key-point: an=a1+(n-1)d
3.代數字:
(1)d=a32=a15+17d,-17=17d,d=-1
(2)a25=a15+10d,-25+10*-1=-35
4.寫答: A:-35
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