8-3-+7=12

-5-9+12=-2

7+9-3=13

-3+8-11=-6

8-3+7=12

(-5)-9+12=-2

7-9-3=-5

(-3)+8-11=-6

a, 8-(3-7)

=8-(-4)

=4

b,(-5)-(9-12)

=(-5)-(-3)

=(-8)

c,7-(-9)-3

=(-2)-3

=-1

d.(-3)+8-11

=5-11

=6

a: \(=\dfrac{5}{9}-\dfrac{12+5}{15}:\dfrac{6}{5}\)

\(=\dfrac{5}{9}-\dfrac{17}{15}\cdot\dfrac{5}{6}=\dfrac{5}{9}-\dfrac{17}{18}=-\dfrac{7}{18}\)

b: \(=\left[\dfrac{6}{5}\left(3+\dfrac{3}{8}-6-\dfrac{5}{8}\right)\right]\cdot\dfrac{5}{6}=-3-\dfrac{1}{4}=-\dfrac{13}{4}\)

a)\(\left(x-y\right)\left(x^3+x^2y+xy^2+y^3\right)=x^4+x^3y+x^2y^2+xy^3-x^3y-x^2y^2-xy^3-y^4=x^4-y^4\)

b) \(x\left(3x-18\right)-3\left(x-4\right)\left(x-2\right)+8=3x^2-18x-3x^2+18x-24+8=-16\)

a: =8-6=2

b: =30(55+46-1)=3000

a) 8 + 2. ( − 3 ) = 8 + ( - 6 ) = 8 - 6 = 2 
b) 30.55 + 30.46 – 2.15

= 30 . 55 + 30 . 46 - 30

= 30 . ( 55 + 46 - 1 )

= 30 . 100 = 3000
c) 4.15 − [ 144 − ( 12 − 4 )² ]

= 4 . 15 - [ 144 - 8² ]

= 4 .15 - [ 144 - 64 ] 

= 60 - 80

= - 20

a: \(=3^2+\left(3^4\right)^{-0.75}-5^{2\cdot0.5}\)

\(=9-5+3^{-3}=4+\dfrac{1}{27}=\dfrac{109}{27}\)

b: \(=2^{4-6\sqrt{7}}\cdot2^{6\sqrt{7}}=2^{4-6\sqrt{7}+6\sqrt{7}}=2^4=16\)

a: \(=x^2-4-x^2+x+8=x+4\)

a) (x-2)(x+2)-x(x-1)+8
= x²-4-x²+x+8
= (x²-x²)+(-4+8)+x
= 4+x
b) bn viết lại đề đi:v
đọc khó quá.

a) Ta có: \(A=\dfrac{2}{3}-\left(-\dfrac{5}{7}+\dfrac{2}{3}\right)\)

\(=\dfrac{2}{3}+\dfrac{5}{7}-\dfrac{2}{3}\)

\(=\dfrac{5}{7}\)

a) \(\left( { - 3} \right).\left( { - 2} \right).\left( { - 5} \right).4\)\( = \left[ {\left( { - 3} \right).\left( { - 2} \right)} \right].\left( { - 5} \right).4\)\( = 6.\left( { - 5} \right).4 =  - 30.4 =  - 120\).

b) \(3.2.\left( { - 8} \right).\left( { - 5} \right)\)\( = 3.2.\left[ {\left( { - 8} \right).\left( { - 5} \right)} \right] = 6.40\)\( = 240\).

\(a,\left(x-2\right)\left(x+3\right)-x\left(x-5\right)=x^2-2x+3x-6-x^2+5x=6x-6\)

\(b,\dfrac{1}{x-2}+\dfrac{-2}{x+2}+\dfrac{2x-8}{x^2-4}=\dfrac{x+2}{\left(x-2\right)\left(x+2\right)}-\dfrac{2\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}+\dfrac{2x-8}{\left(x+2\right)\left(x-2\right)}=\dfrac{x+2}{\left(x-2\right)\left(x+2\right)}-\dfrac{2x-4}{\left(x+2\right)\left(x-2\right)}+\dfrac{2x-8}{\left(x+2\right)\left(x-2\right)}=\dfrac{x+2-2x+4+2x-8}{\left(x+2\right)\left(x-2\right)}=\dfrac{x-2}{\left(x+2\right)\left(x-2\right)}=\dfrac{1}{x+2}\)