tra loi nhanh ho mk voi

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)

    = \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\)

      = \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)

      = \(1-\frac{1}{7}\)

      =   \(\frac{7}{7}-\frac{1}{7}\)

        = \(\frac{6}{7}\)

2) \(\frac{7}{4}-x.\frac{4}{3}=\frac{5}{19}\)

              \(x.\frac{4}{3}=\frac{7}{4}-\frac{5}{19}\)

         \(x.\frac{4}{3}=\frac{133}{76}-\frac{20}{76}\)

\(x.\frac{4}{3}=\frac{113}{76}\)

      \(x=\frac{113}{76}:\frac{4}{3}\)

      \(x=\frac{399}{304}\)

VẬY \(x=\frac{399}{304}\)

b) \(\left(x+\frac{3}{4}\right).\frac{5}{7}=\frac{10}{9}\)

      \(\left(x+\frac{3}{4}\right)=\frac{10}{9}:\frac{5}{7}\)

     \(x+\frac{3}{4}=\frac{14}{9}\)

              \(x=\frac{14}{9}-\frac{3}{4}\)

               \(x=\frac{29}{36}\)

Vậy \(x=\frac{29}{36}\)

c) \(x.\frac{1}{2}+\frac{3}{2}.x=\frac{4}{5}\)

\(x.\left(\frac{1}{2}+\frac{3}{2}\right)=\frac{4}{5}\)

\(x.2=\frac{4}{5}\)

     \(x=\frac{4}{5}:2\)

      \(x=\frac{2}{5}\)

Vậy \(x=\frac{2}{5}\)

Chúc bạn học tốt !!!

dung roi,cam on ban nhieu

a,x/12-1/3=3/4

x/12         =3/4+1/3

x/12         =13/12

vậy x =13

b,3/4-x=5/12

         x=3/4-5/12

         x=4/12=1/3

c,x nhân 2/3-1/3=1/4

x nhân 2/3         =1/4+1/3

x nhân 2/3         =7/12

x                        =7/12 : 2/3

x                        =21/24=7/8

d,5/7-(x-1/2)=1/7

x-1/2            =5/7-1/7

x -1/2           =4/7

x                  =4/7+1/2

x                  =15/14

bạn nhớ k cho mình nhé!

ai nhNH MK K

#maianhhappy

bài 1 tính giá trị biểu thức

( - 25 ) nhân ( -3 ) nhân x với x = 4

\(\left(-25\right).\left(-3\right).4\)

\(=\left(-25\right).4.\left(-3\right)\)

\(=-100.\left(-3\right)=300\)

( -1 ) nhân ( -4 ) nhân 5 nhân 8 nhân y với y =25

\(\left(-1\right).\left(-4\right).5.8.25\)

\(=4.5.8.25=4.25.5.8\)

\(=100.40=40000\)

( 2ab mũ 2 ) : c với a =4 ; b= -6 ; c =12

\(\left(2.4.\left(-6\right)\right)^2:12\)

\(=\left(-48\right)^2:12\)

\(=2304:12=192\)

[ ( -25 ) nhân ( - 27 ) nhân ( -x ) ] : y với x = 4 ; y = -9

\(\left[\left(-25\right).\left(-27\right).\left(-4\right)\right]:-9\)

\(=-2700:\left(-9\right)\)

\(=300\)

(a mũ 2 _ b mũ 2) : ( a + b ) nhân ( a _ b ) với a + 5 , b = -3

\(\left(5^2-\left(-3\right)^2\right):\left(5-3\right).\left(5+3\right)\)

\(=16:2.8\)

\(=8.8=64\)

bài 2 tìm x

( 2x _ 5 ) + 17 = 6

\(2x-5=-11\)

\(2x=-6\)

\(x=-3\)

10 _ 2 ( 4 _ 3x ) = - 4

\(2.\left(4-3x\right)=14\)

\(4-3x=7\)

\(3x=-3\)

\(x=-1\)

- 12 + 3 ( -x + 7 ) = -18

\(3\left(-x+7\right)=-6\)

\(-x+7=-2\)

\(-x=-9\)

\(x=9\)

24 : ( 3x _ 2 ) = -3

\(3x-2=-8\)

\(3x=-6\)

\(x=-2\)

- 45 : 5 nhân ( -3 _ 2x ) = 3

\(5.\left(-3-2x\right)=-15\)

\(-3-2x=-3\)

\(2x=0\)

\(x=0\)

`75/20 - x = 3/2 xx 10`

`15/4 - x = 15`

              `x  = 15/4 - 15`

              `x  = -45/4`

`(12 xx 15) - X xx 1/4 = 120 xx 1/4`

 `180 - X xx 1/4    = 30`

            `X xx 1/4   = 180-30`

            `X xx 1/4   = 150` 

                     `X     = 150 : 1/4`

                     `X      = 600`

\(\dfrac{15}{4}-x=15\)

\(x=\dfrac{15}{4}-15\)

\(x=-\dfrac{45}{4}\)

\(\left(12\times15\right)-\dfrac{1}{4}x=120\times\dfrac{1}{4}\)

\(180-\dfrac{1}{4}x=30\)

\(-\dfrac{1}{4}x=30-180\)

\(-\dfrac{1}{4}x=-150\)

\(-x=-150:\dfrac{1}{4}\)

\(-x=-150\times4\)

\(-x=-600\)

\(x=600\)

75/20 - X = 3/2 x 10

75/20 - X = 15

X = 75/20 - 15 

X = -45/4.

( 12 x 15  ) -  x X 1/4 = 120 x 1/4

( 12 x 15  ) -  x X 1/4 = 30

180 -  x X 1/4 = 30

180 -1/4X = 30

-1/4X = 30 - 180

-1/4X = -150

X = -150 x -4

X = 600.

\(a,\left(x-1\right)^2-2^2=\left(x-1-2\right)\left(x-1+2\right)=\left(x-3\right)\left(x+1\right)\\ b,=\left(2x\right)^2+2.2x.3+3^2\\ =\left(2x+3\right)^2\\ c,=x^3-\left(2y\right)^3\\ =\left(x-2y\right)\left(x^2+2xy+4y^2\right)\\ d,=x^3\left(x^2-1\right)-\left(x^2-1\right)\\ =\left(x^3-1\right)\left(x^2-1\right)\\ =\left(x-1\right)\left(x^2+x+1\right)\left(x-1\right)\left(x+1\right)\\ =\left(x-1\right)\left(x+1\right)\left(x^2+x+1\right)\)

\(e,=-4x^2\left(x-1\right)+\left(x-1\right)\\ =\left(1-4x^2\right)\left(x-1\right)\\ =\left(1-2x\right)\left(1+2x\right)\left(x-1\right)\)

\(f,=\left(2x\right)^3+3.\left(2x\right)^2.1+3.2x.1^2+1^3\\ =\left(2x+1\right)^3\)

1/(x+2)(x+3)(x+4)(x+5)-24

=(x+2)(x+5)(x+3)(x+4)

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

=[(x+2)(x-2)+7x+14][(x+3)(x-3)+7x+21]

=(x²-4+7x+14)(x²-9+7x+21)

=(x²+10+7x)(x²+12+7x)

2/(x²+x)²+4(x²+x)-12

=(x²+x)²+4(x²+x)+2²-16

=(x²+x+2)²-4²

=(x²+x+2+4)(x²+x+2-4)

=(x²+x+6)(x²+x-2)

3/(x²+x+1)(x²+x+2)-12

=(x²+x+1)(x²+x+-1+3)-12

=(x²+x+1)(x²+x+-1)+3(x²+x+1)-12

=(x²+x)-1+3(x²+x)+3-12

=(x²+x)(x²+x+3)-10

làm đến đây thì mk bí, bạn giúp suy nghĩ nốt nha

4/nó là nhân tử sẵn rồi mà

\(3/\)

\(\left(x^2+x+1\right)\left(x^2+x+2\right)-12\)

\(=\left(x^2+x+1\right)\left(x^2+x+1+1\right)-12\)

\(=\left(x^2+x+1\right)^2+x^2+x+1-12\)

\(=\left(x^2+x+1\right)^2+4\left(x^2+x+1\right)-3\left(x^2+x+1\right)-12\)

\(=\left(x^2+x+1\right)\left(x^2+x+1+4\right)-3\left(x^2+x+1+4\right)\)

\(=\left(x^2+x+1-3\right)\left(x^2+x+1+4\right)\)

\(=\left(x^2+x-2\right)\left(x^2+x+5\right)\)