Question

Diana

為什麼240/5會等於a5？

8. 一等差數列,an表第n項,若ay+ as + as+ a7+ ay= 240,az+ aat a + as+ a10=
220,則:
(1)此數列的公差為何? 4
ANE
(2) a₁ = ?
dit die =
a₁ taz tas tan tag = 240-0
A₂+ay+ ab +as+ Ap=220 - @
- D
d+d+d+d+d=
240
200
440
230
2/480
2
5d=-20
4pc
d = -4
as = a₁ +4d
=
240
5.
加到正数軌,姑小

Answer 1

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chou014

a1 + a3 + a5 + a7 + a9 = 240
那全部用首項 + 公差的形式表示的話就會變成
a1 + (a1 + 2d) + (a1 + 4d) + (a1 + 6d) + (a1 + 8d) = 240
5a1 + 20d = 240
a1 + 4d = 240 / 5

Diana

謝謝你我懂了🙏