(a+2x)^5=a^5+5a^4(2x)+10a^3(2x)^2+...
40a^3=40???
(a+2x)^5=a^5+5a^4(2x)+10a^3(2x)^2+...
40a^3=40???
john24d2003 發表於 16-5-2011 01:26 http://www.nakuz.com/bbs/images/common/back.gif
你可唔可以用英文解一次比我聽-_- 我睇唔明個d系數...正數解...:L
本帖最後由 john24d2003 於 16-5-2011 22:36 編輯
你可唔可以用英文解一次比我聽-_- 我睇唔明個d系數...正數解...
vin712 發表於 16-5-2011 01:33 http://www.nakuz.com/bbs/images/common/back.gif
爆開你應該識
say for example,(2+2x^2)^2=4+8x^2+4x^4
x^4 term=4x^4
coefficient of x^4(系數)=4
constant term=4
coefficient of x^3=0 (without x^3 term)
Method 1:
(a+2x)^5
=(5C0)(a^5)(2x)^0+(5C1)(a^4)(2x)^1+(5C2)(a^3)(2x)^2+(5C3)(a^2)(2x)^3+(5C4)(a^1)(2x)^4+(5C5)(a^0)(2x)^5
=a^5+(10a^4)x+(40a^3)x^2+(80a^2)x^3+80ax^4+32x^5
so,
40a^3=40
a^3=1
a=1
=====================================================
Method 2:
the (r+1)th term
=(5Cr)(a^r)[(2x)^(5-r)]
=(5Cr)(a^r)
To find the coefficient of x^2
5-r=2 , i.e.r=3
So the coefficient of x^2
=(5C3)(a^3)
=(10)(a^3)(4)
=40a^3
so,
40a^3=40
a^3=1
a=1
本帖最後由 vin712 於 16-5-2011 18:40 編輯
爆開你應該識
say for example,(2+2x^2)^2=4+8x^2+4x^4
x^4 term=4x^4
cofficient of x^4(系數)=4
con ...
john24d2003 發表於 16-5-2011 02:01 http://www.nakuz.com/bbs/images/common/back.gif
喔..thx...其實我今日都問左呀sir..佢解左比我聽係咩黎v_v
上完m2堂自不然老師就會比d題目我地返去做a___a,但系有d題目未教過=.=
1.已知在(a+2x)^5的展開式中,x^2的係 ...
_銘記於心` 發表於 16-5-2011 00:21 http://www.nakuz.com/bbs/images/common/back.gif
假若你仲記得d次方既pattern既話 你應該會搵到40a^3 x^2
咁姐係40a^3 = 40
a=1
唔明再問or睇5樓@@
Method 1:
(a+2x)^5
=(5C0)(a^5)(2x)^0+(5C1)(a^4)(2x)^1+(5C2)(a^3)(2x)^2+(5C3)(a^2)(2x)^3...
maxycy 發表於 16-5-2011 09:22 http://www.nakuz.com/bbs/images/common/back.gif
條題目問到X^2
唔使爆到咁大
有X^2term就可以+...
本帖最後由 john24d2003 於 16-5-2011 22:44 編輯
明白了!但系5c=階x記法?!
_銘記於心` 發表於 16-5-2011 22:36 http://www.nakuz.com/bbs/images/common/back.gif
del...