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a) A = ( a+ b – c + d ) – ( - a – b + c – d )
= a+ b – c + d + a + b - c + d
= 2a + 2b + 2d – 2c
b) B = ( a+ b – c ) + ( a – b ) – ( a – b - c )
= a+ b – c + a – b – a + b + c
= a + b
a) ( a + b + c ) - ( a - b - c )
= ( a + b + c ) - a + b + c
= a + ( - a ) + b + c + b + c
= 0 + b + c + b + c
= ( b + c ) x 2
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 + 0
= a + b
c) - ( a - b - c ) + ( -a + b - c ) - ( -a + b + c )
= ( -a ) + b + c + ( -a ) + b - c + a - b - c
= [ ( -a ) + ( -a ) + a ] + [ b + b + ( -b ) ] + [ c + ( -c ) + ( -c ) ]
= ( -a ) + b + ( -c )
a , ( a + b + c ) - ( a - b - c )
= a + b + c - a + b + c
= ( a - a ) b + b + c + c
= 0 + b + b + c + c
= 0 + 2b + 2c
= 0 + 2(b + c )
= 2(b+c)
b , ( a + b - c ) + ( a - b ) - ( a - b - c )
= a + b - c + a - b - a + b + c
= ( a - a ) + b + b + ( - c + c )
= 0 + b + b + 0
= 2b
c , - ( a - b - c ) + ( - a + b - c ) - ( - a + b + c )
= - a + b + c - a + b - c + a - b - c
= ( - a + a ) + ( b - b ) + ( c - c ) + a + b
= 0 + 0 + 0 + a + b= a + b
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
=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
A = ( a+ b – c + d ) – ( - a – b + c – d )
= a+ b – c + d + a + b - c + d
= 2a + 2b + 2d – 2c