1. If(x+7)(2x-5)=Ax^2+Bx+C,find the values of A,B and C
2.A(5-x)=2(Bx+45),find the values of A and B
3.A(x-5)+B(x+7)=3x-12,find the values of A and B
F.2 數學 identity
2009-12-30 6:23 am
回答 (2)
2009-12-30 9:00 am
✔ 最佳答案
1)(x+7)(2x-5)=Ax^2+Bx+CLHS = 2x^2 + 14x - 5x - 35
= 2x^2 + 9x - 35
So A = 2 , B = 9 , C = - 35
2)A(5-x)=2(Bx+45)
-Ax + 5A = 2Bx + 90
So -A = 2B...(1)
5A = 90...(2)
By (2) , A = 18 ,sub it to (1):
-18 = 2B , B = - 9
3.A(x-5)+B(x+7)=3x-12
when x = 5 ,
0 + B(5+7) = 3*5 - 12
12B = 3
B = 1/4
when x = - 7 :
A(-7-5) + 0 = 3(-7) - 12
-12A = - 33
A = 11/4
2010-01-01 5:24 am
收錄日期: 2021-04-21 22:06:58
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https://hk.answers.yahoo.com/question/index?qid=20091229000051KK02260