For the expression a(x^2) + bx + 25, write down two possible sets of the values of a and b such that the expression is a perfect square.
這題我已經問過了,
http://hk.knowledge.yahoo.com/question/question?qid=7008080401917
但還未有滿意答案,
所以想再問多次...
我不明白什麼是delta(Δ),
加上他們又沒有詳細步驟,
使我不明白為何會這樣變左那樣...
有高手可以解釋得清楚些嗎?
或者有否其他方法計算?
thx~~~!!!
Math question(f.2-f.3) 20marks
2008-08-13 2:00 am
回答 (2)
2008-08-13 2:39 am
✔ 最佳答案
As follows: As follows: As follows: As follows:圖片參考：http://i277.photobucket.com/albums/kk75/uncle_michael/080812_mat_3.jpg?t=1218537445
2008-08-13 2:59 am
delta(Δ) or discriminant, 是中4 Additional mathematics 教的东西...用来判断quadratic equation(１元２次方程)的roots (根，即答案)
e.g. x^2 - 5x 4 = 0 , x= roots , x=1 or 4 (notice that a quadratic equation has 2 roots (2 solutions)
a(x^2) bx 25 , 在你所学的技巧上，只能用'撞' 的方法
First, suppose x =1
a b 25= a perfect square
set 1, 25 is already perfect square, a=0 , b=0
set 2, 100 is a perfect square , a b 25=100
a b= 75
a=25 , b=50
check set 2: if x =2, the expression a(x^2) bx 25 = a perfect square
if x=3, the expression a(x^2) bx 25 = a perfect square
So, a=0,b=0 and a=25,b=50 are 2 possible sets of the values of a and b.
In fact , you have to memorize that a must be a perfect square when you do such kind of question.
e.g. x^2 - 5x 4 = 0 , x= roots , x=1 or 4 (notice that a quadratic equation has 2 roots (2 solutions)
a(x^2) bx 25 , 在你所学的技巧上，只能用'撞' 的方法
First, suppose x =1
a b 25= a perfect square
set 1, 25 is already perfect square, a=0 , b=0
set 2, 100 is a perfect square , a b 25=100
a b= 75
a=25 , b=50
check set 2: if x =2, the expression a(x^2) bx 25 = a perfect square
if x=3, the expression a(x^2) bx 25 = a perfect square
So, a=0,b=0 and a=25,b=50 are 2 possible sets of the values of a and b.
In fact , you have to memorize that a must be a perfect square when you do such kind of question.
參考: Myself
收錄日期: 2021-04-13 15:56:33
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080812000051KK02236