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![](https://rs.olm.vn/images/avt/0.png?1311)
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)
![](https://rs.olm.vn/images/avt/0.png?1311)
Xét tổng
Suy ra có ít nhất một trong 7 số |
là số chẵn
![](https://rs.olm.vn/images/avt/0.png?1311)
E=(-a-b+c+d)-(d+c-b-2a)
E=-a-b+c+d-d-c+b+2a
E=-a+(-)b+c+d+(-d)+(-c)+b+2a
E=-a+(-b)+c+d+(-d)+(-c)+b+2a
E=(2a-a)+(-b+b)+(-d+d)+(-c+c)=a+0+0+0=a
![](https://rs.olm.vn/images/avt/0.png?1311)
a, A=(a-b)-(a-b+c)
=a-b-a+b-c
=(a-a)+(b-b)-c
= 0 + 0 - c
=-c
b, B=(a+b+c)-(a+b-c)
=a+b+c-a-b+c
=(a-a)+(b-b)+(c+c)
=0+0+2c
=2c
t**k cho mình nha!!
chúc hok tốt!!
![](https://rs.olm.vn/images/avt/0.png?1311)
=a+c+d+c-b-d+b-d+c-a
=(a-a)+(b-b)+(c+c+c)+(d-d-d)
=0+0+3c-d
=3c-d
-(a-c-d)-(-c+b+d)+(b-d+c-a)
=-a+c+d+c+b+d+b-d+c-a
=(-a-a)+(c+c+c)+(d+d-d)+(b+b)
=-2a+3c+d+2b
Vay = -2a+3c+d+2b
![](https://rs.olm.vn/images/avt/0.png?1311)
a)A=(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
b)B=(-a-b+c)+(a+b)
=-a-b+c+a+b
=(-a+a)-(b-b)+c
=0+0+c=c
c)C=-(a+b-c)+(-c)+(-a-b)-(a+b+c)
=-a+b-c-c-a-b-a+b+c
=-(a+a+a)+(b-b+b)-(c+c-c)
=-3a+b-c
d)D=-(-a-b)-(b+c)+(c-a+b)-(b-a-c)
=a+b-a+c+c-a+b-b+a+c
=(a-a+a)-(b-b+b)+(c+c+c)
=a-b+3c
\(a,A=\left(a+b-c\right)+\left(a-b\right)-\left(a-b-c\right)\)
\(=a+b-c+a-b-a+b+c\)
\(=a+b\)
\(b,B=\left(-a-b+c\right)+\left(a+b\right)\)
\(=-a-b+c+a+b\)
\(=c\)
\(c,C=-\left(a+b-c\right)+\left(-c\right)+\left(-a-b\right)-\left(a+b+c\right)\)
\(=-a-b+c-c-a-b-a-b-c\)
\(=-3a-3b-c\)
câu d cũng tương tự nha
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
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)
= 0 + 2b + 0 + 2d = 2(b + d).
b) -(a + b + c + d) + (a - d) - (-b + c)
= -a - b - c - d + a - d - b - c
= -a + (-b) + (-c) + (-d) + a + (-d) + (-b) + (-c)
= -2(b + c + d).
c) -(a - b - d) + (b -c + d) - (-c + b + d)
= -a + b + d + b + (-c) + d - c - b - d
= -a + b + d + (-2c).
d) -(a - b - c) + (-a - b - c) - (-a -b + c)
= -a + b + c + (-a) - b - c - a + b - c
= -3a + b + (-c).
![](https://rs.olm.vn/images/avt/0.png?1311)
B1:
a) \(\left(a+b+c+d\right)-\left(a-b+c-d\right)\)
\(=a+b+c+d-a+b-c+d\)
\(=\left(a-a\right)+\left(b+b\right)+\left(c-c\right)+\left(d+d\right)\)
\(=2b+2d\)
\(=2\left(b+d\right)\)
b) \(-\left(a+b+c+d\right)+\left(a-d\right)-\left(-b+c\right)\)
\(=-a-b-c-d+a-d+b-c\)
\(=\left(-a+a\right)-\left(b-b\right)-\left(c+c\right)-\left(d+d\right)\)
\(=0-2c-2d\)
\(=-2c-2d\)
\(=2\left(-c-d\right)\)
c) \(-\left(a-b-d\right)+\left(b-c+d\right)-\left(-c+b+d\right)\)
\(=-a+b+d+b-c+d+c-b-d\)
\(=-a+\left(b+b-b\right)+\left(d-d\right)-\left(c-c\right)\)
\(=-a+b\)
d) \(-\left(a-b-c\right)+\left(-a-b-c\right)-\left(-a-b+c\right)\)
\(=-a+b+c+\left(-a\right)-b-c-a+b-c\)
\(=\left(-a+-a\right)+\left(b-b\right)+\left(c-c-c\right)\)
\(=-2a+-c\)
Bài 2:
b) \(-1-2-3-...-2002=-\left(1+2+3+...+2002\right)\)
... ( tự tính )
B3: Tự tính
B4:
a) Có \(-a+b=-\left(a-b\right)\)
Mà \(a-b\) là số đối của \(-\left(a-b\right)\)
\(\Rightarrow a-b\) là số đối của \(-a+b\)
b) \(-a+b-c=-\left(a-b+c\right)\) ( đpcm )
![](https://rs.olm.vn/images/avt/0.png?1311)
-(a - b + c) - (-a + b - c) + (-a - c - 2b)
= -a + b - c + a - b + c - a - c - 2b
= (-a + a - a) + (b - b - 2b) + (-c + c - c)
= -a - 2b - c
a,M=(a+b+c-d)+(a-b+c-d)=a+b+c-d+a-b+c-d=2a+2c-2d=2(a+c-d)
b,-(a+b-c)+(a-b-c)
-a-b+c+a-b+c=-2b (ĐPCM)
hok tút
b) -(a + b - c) + (a - b - c)
= -a - b + c + a - b - c
= (-a + a) - (b + b) + (c - c)
= 0 - 2b + 0
= -2b