\(a,=a-b+c-d-a-b-c-d=-2b-2d\\ b,=-a+b-c+a-b-a+b-c=-a+b-2c\)

a) ( a - b + c -d ) - ( a+ b + c + d ) = a - b + c - d - a - b - c - d = -2b - 2d 

b) ( -a + b -c ) + ( a - b ) - ( a- b + c ) = -a + b - c + a - b - a + b - c = -a + b - c - c = -a + b - 2c 

c) - ( a - b - c ) + ( b - c + d ) - ( -a + b + d )

a) (a - b + c - d) - (a + b - + c + d) = a - b + c - d - a - b + c - d = -2b + 2c - 2d

b) (-a + b - c) + (a - b) - ( a - b + c) = -a + b - c + a - b - a + b - c = -a + b - 2c

c) -(a - b - c) + (b - c + d) - (a - b + c) = -a + b + c + b - c + d - a + b - c = -2a + 3b - c + d

`@` `\text {Ans}`

`\downarrow`

`a)`

`(a -b + c- d) - ( a+ b- +c+d)`

`= a - b + c - d - a - b + c - d`

`= (a-a) + (-b-b) + (c+c) + (-d-d)`

`= -2b + 2c - 2d`

`b)`

` ( -a + b - c) + ( a - b) - (a - b + c)`

`= -a + b - c + a - b - a + b - c`

`= (-a +a - a) + (b - b + b) + (-c-c)`

`= a + b - 2c`

`c)`

\( – ( a- b- c) + ( b – c+d) – ( a-b +c)\)

`= - a + b + c + b - c + d - a + b - c`

`= (-a -a) + (b + b + b) + (c-c-c) + d`

`= -2a + 3b - c + d`

B1:

a,  a+b+(-a)+b+a+(-c)+(-a)+(-c)=[a+(-a)+a+(-a)]+(b+b)+[(-c)+(-c)]=0+2.b+(-2).c

b,  a+b+(-c)+a+(-b)+c+(-b)+(-c)+a+(-a)+b+c=[a+a+a+(-a)]+[b+(-b)+(-b)+b]+[(-c)+c+(-c)+c]=2.a+0+0=2a

B2:

N=(a+b)-(a-b)+(a+b)=a+b+(-a)+b+a+b=[a+(-a)+a)+(b+b+b)=a+3.b

NẾU CẬU KHÔNG HIỂU THÌ CỨ HỎI NHÉ!

rút gọn biểu thức

a,A=(a-b)-(a-b+c)

b,B=-(a+b+c)-(a+b-5)

A = 2x-3 -x+5 = x+2

A = 2x -3 +x-5 = 3x -8

câu B cũng có 2 truong hop tuong tu

\(a,\left(a+b-c\right)-\left(a-b+c\right)\)

\(=a+b-c-a+b-c\)

\(=2b-2c\)

\(=2\left(b-c\right)\)

\(b,\) Thay \(a=5,b=7,c=8\) vào biểu thức

\(\Rightarrow\left(5+7-8\right)-\left(5-7+8\right)=-2\)