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Mathematical problems in seventh grade in America
Calculation:

-8m? -【4m-2m? -(3m-2m? -7)]

=-8m? -(4m-2m? -3m+2m? +7)

=-8m? -4m+2m? +3m-2m? -7

=(-8m? +2m? -2m? )-4m-7

=-8m? -4m-7

3x? -[7x-(4x-3)-2x? ]

=3x? -(7x-4x+3-2x? )

=3x? -7x+4x-3+2x?

=(3x? +2x? )+(-7x+4x)-3

=5x? 3x 3

1/2(a? -b)+ 1/3(a-b? )+ 1/6(a? +b? )

= 1/2a? - 1/2 b+ 1/3a- 1/3b? + 1/6a? + 1/6b?

=( 1/2a? + 1/6a? )- 1/2 b+ 1/3a+(- 1/3b? + 1/6b? )

=2/3a? - 1/2 b+ 1/3a- 1/6b?

5ab? -3【2a? -2(a? b-2ab? )]

=5ab? -3(2a? -2a? b+4ab? )

=5ab? -6a? +6a? b- 12ab?

=(5ab? - 12ab? )-6a? +6a? b

=-7ab? -6a? +6a? b

Simplify first, then evaluate

1/4(-4x? +2x-8)-( 1/2x- 1), where x= 1/2.

=-x? + 1/2x-2- 1/2x+ 1

=-x? - 1

=-( 1/2)? - 1

=- 1/4- 1

=-5/4

(4a? -3a)-(2a? +a- 1)+(2-a? +4a), where a=-2

=4a? -3a-2a? -a+ 1+2-a? +4a

=(4a? -2a? -a? )+(-3a-a+4a)+( 1+2)

=a? +3

=(-2)? +3

=4+3

=7

A-2(2a+b)+3(a-b), where a=-2.

=a-4a-2b+3a-3b

=(a-4a+3a)-(2b+3b)

=-5b

=-5×(-2)

= 10

4x? -(2x? +x- 1)+(2-x? -3x), where x=- 1/2

=4x? -2x? -x+ 1+2-x? -3 times

=(4x? -2x? -x? )-(x+3x)+( 1+2)

=x? -4x+3

=(- 1/2)? -4×(- 1/2)+3

= 1/4+2+3

=2 1/4

5(3a? b-ab? )-(ab? +3a? B) where a = 1/2 and b =- 1.

= 15a? b-5ab? -ab? -3a? b

=( 15a? b-3a? b)-(5ab? +ab? )

= 12a? b-6ab?

= 12×( 1/2)? ×(- 1)-6× 1/2×(- 1)?

= 12× 1/4×(- 1)-6× 1/2× 1

=-3-3

=-6

Is called A=4a? +5b,B=-3a? -2b, find the value of 2A-B, where a =-2 and b = 1.

2A-B

=2(4a? +5b)-(-3a? -2b)

=8a? + 10b+3a? +2b

= 1 1a? + 12b

= 1 1×(-2)? + 12× 1

= 1 1×4+ 12

=56

Known (x+ 1)? +|y- 1|=0, find 2(xy-5xy? )-(3xy? -xy) value.

∫(x+ 1)? +|y- 1|=0

∴x+ 1=0 and y- 1=0.

∴x=- 1,y= 1

2(xy-5xy? )-(3xy? -xy)

=2xy- 10xy? -3xy? +xy

=3xy- 13xy?

=3×(- 1)× 1- 13×(- 1)× 1?

=-3+ 13

= 10

Is called A=x? +2x? y+2y? - 1,B=3+y? +2x? y+2x? If A+B+C=0, find c.

A+B+C=0

C=-(A+B)

C=-(x? +2x? y+2y? - 1+3+y? +2x? y+2x? )

=-x? -2x? y-2y? + 1-3-y? -2x? y-2x?

=-(x? +2x? )-(2x? y+2x? y)-(2y? +y? )+( 1-3)

=-3x? -4x? y-3y? -2