✔ 最佳答案
我本暑期作業要我:
9.簡化以下代數式
(a)3r+4s-2r+7s,
3r+4s-2r+7s = 3r - 2r + 4s + 7s = (3-2)r + (4+7)s
= r + 11s
(b)4x二次方-2x+7-2x+3x二次方+5x-2
4x^2 - 2x + 7 -2x + 3x^2 + 5x - 2 = 4x^2 + 3x^2 - 2x -2x + 5x + 7 - 2 = (4+3)x^2 + (5-2-2)x + (7-2)
= 7x^2 + x + 5
(c)a+2b+3c+4a-6b-2c
a + 2b + 3c + 4a - 6b - 2c = a + 4a + 2b - 6b + 3c - 2c = (1+4)a + (2-6)b + (3-2)c
= 5a - 4b + c
(d)2xy+3x-2y+4x-6y+5xy
2xy + 3x - 2y + 4x - 6y + 5xy = 2xy + 5xy + 3x + 4x - 2y - 6y = (2+5)xy + (3+4)x + (-2-6)y
= 7xy + 7x - 8y
改正下列計算中的錯誤:
1. 2x+3x二次方+x-2x二次方 ======> 2x + 3x^2 + x - 2x^2
=3x+x二次方
=4x三次方 (THIS IS WRONG, because x and x^2 are different terms, and you can't add them up)
2. 8x+4 /2-(3x-2) [IS IT (8X+4)/2 - (3X-2) ? OR 8x + 4/2 - (3x-2)??]
=4x+4-3x-2
=x+2
3. 5(a-1)/2 - 4(a+1)/3
=15(a-1)-8(a+1) (THIS IS WRONG HERE, because it should be 15(a-1)/6 - 8(a+1)/6 => [15a-15-8a-8]/6 => (7a-23)/6)
=15a-15-8a-8
=7a-23
2008-07-24 00:29:21 補充：
(8X+4)/2-(3X-2)
=4x+4-3x-2 ==>(8x+4)/2=4x+2,not 4x+4 and -(3x-2)=-3x+2,not -3x-2
(8X+4)/2-(3X-2)becomes:4x+2-3x+2=(4-3)x+2+2=x+4
2008-07-24 00:29:30 補充：
(a)3x+x-2x=(3+1-2)x=2x
(b)5m-5-2(2m+1)=5m-5-(4m+2)=5m-5-4m-2=(5-4)m-5-2=m-7
(c)(2m+5/2)-(m-1/4)=2m+5/2-m+1/4=(2-1)m+5/2+1/4=m+11/4
(d)6x(2a+7/3)+4x(3a-5/2)=(12ax+14x)+(12ax-10x)=24ax+4x
