x.3,7+x.6,3=120b,x.3,7+x.6,3=120

x(3,7+6,3)=120x(3,7+6,3)=120

10x=12010x=120

x=120:10x=120:10

x=12(tm)

 (15×24-x):0.25=100 : 1/4

(15×24-x):0.25 = 400

(15x24-x) = 100

360-x =100

x=260

(8.75+1.25 +5+1) x X=20

16 x X=20

X=20 :16

X=1.25

nhớ tít

a, \(\left(\frac{1}{2}xy-\frac{3}{4}\right)\left(\frac{1}{2}xy+\frac{3}{4}\right)=\frac{1}{4}x^2y^2+\frac{3}{8}xy-\frac{3}{8}xy-\frac{9}{16}=\frac{1}{4}x^2y^2-\frac{9}{16}\)

b, \(\left(2x+3\right)\left(4x^2-6x+9\right)=8x^3-12x^2+18x+12x^2-18x+27=8x^2+27\)

c, \(\left(xy-2\right)\left(x^2y^2+2xy+4\right)=x^3y^3+2x^2y^2+4xy-2x^2y^2-4xy-8=x^3y^3-8\)

Mk ko chép đề bài ra nhé

a, = 1/2xy.( -3/4 + 3/4 )

   =1/2xy.

b, Áp dụng HĐT số 2, có:  (Chỗ này ko cần chép cx đc)

=(2x+3).(2x+3)^2  (^ là mũ)

=(2x+3)^3

c, Áp dụng HĐT số 2, có:

=(xy-2).(xy + 2)^2

\(\left(x-36\right):18=3\Leftrightarrow x-36=54\Leftrightarrow x=90\)

\(415-9\left(x+2\right)=2^2.5^2\Leftrightarrow415-9\left(x+2\right)=100\Leftrightarrow9\left(x+2\right)=315\Leftrightarrow x+2=35\Leftrightarrow x=33\)

\(5\left(4+6x\right)=290\Leftrightarrow4+6x=58\Leftrightarrow6x=54\Leftrightarrow x=9\)

             Bài làm :

\(\left(x-36\right)\div18=3\)

\(\Leftrightarrow x-36=3\times18\)

\(\Leftrightarrow x-36=54\)

\(\Leftrightarrow x=54+36=90\)

\(415-9\times\left(x+2\right)=2^2\times5^2\)

\(\Leftrightarrow415-9\times x-9\times2=\left(2\times5\right)^2\)

\(\Leftrightarrow415-9\times x-18=10^2\)

\(\Leftrightarrow397-9\times x=100\)

\(\Leftrightarrow9\times x=397-100\)

\(\Leftrightarrow9\times x=297\)

\(\Leftrightarrow x=297\div9=33\).

\(5\times\left(4+6\times x\right)=290\)

\(\Leftrightarrow4+6\times x=290\div5\)

\(\Leftrightarrow4+6\times x=58\)

\(\Leftrightarrow6\times x=58-4\)

\(\Leftrightarrow6\times x=54\)

\(\Leftrightarrow x=54\div6=9\)

Chúc bạn học tốt !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

a) MgCO₃+2HCl - MgCl₂+CO₂+H₂O

          n_MgCO3= 21/81=0,25 mol

Theo p/trình cứ

     1 mol MgCO₃ - 2 mol HCl - 1 mol MgCl₂

       0,25 mol  -   0,5 mol -  0,5 mol

b) V_HCl= 0,5/2=0,25l

c) m_MgCl2= 0,5*95=47,5g

a) ( 3x + 2 )( x - 1 ) - ( x + 2 )( 3x + 1 ) = 7

<=> 3x² - x - 2 - ( 3x² + 7x + 2 ) = 7

<=> 3x² - x - 2 - 3x² - 7x - 2 = 7

<=> -8x - 4 = 7

<=> -8x = 11

<=> x = -11/8

b) ( 6x + 5 )( 2x + 3 ) - ( 4x + 3 )( 3x - 2 ) = 8

<=> 12x² + 28x + 15 - ( 12x² + x - 6 ) = 8

<=> 12x² + 28x + 15 - 12x² - x + 6 = 8

<=> 27x + 21 = 8

<=> 27x = -13

<=> x = -13/27 

c) 2x( x + 3 ) - ( x + 1 )( 2x + 1 ) - 5 = 9

<=> 2x² + 6x - ( 2x² + 3x + 1 ) - 5 = 9

<=> 2x² + 6x - 2x² - 3x - 1 - 5 = 9

<=> 3x - 6 = 9

<=> 3x = 15

<=> x = 5

d) ( 5x + 3 )( 4x - 7 ) - ( 10x + 9 )( 2x - 3 ) = 10

<=> 20x² - 23x - 21 - ( 20x² - 12x - 27 ) = 10

<=> 20x² - 23x - 21 - 20x² + 12x + 27 = 10

<=> -11x + 6 = 10

<=> -11x = 4

<=> x = -4/11

a, \(\left(3x+2\right)\left(x-1\right)-\left(x+2\right)\left(3x+1\right)=7\Leftrightarrow-8x-4=7\Leftrightarrow x=-\frac{11}{8}\)

b, \(\left(6x+5\right)\left(2x+3\right)-\left(4x+3\right)\left(3x-2\right)=8\Leftrightarrow27x+21=8\Leftrightarrow x=-\frac{13}{27}\)

c, \(2x\left(x+3\right)-\left(x+1\right)\left(2x+1\right)-5=9\Leftrightarrow3x-6=9\Leftrightarrow x=5\)

d, \(\left(5x+3\right)\left(4x-7\right)-\left(10x+9\right)\left(2x-3\right)=10\Leftrightarrow-11x+6=10\Leftrightarrow x=-\frac{4}{11}\)

 Put in been or gone.

1. Jim is on holiday. he has GONE to Italy
2.Hello ! I've just BEEN to the shops. I've bought lots of things
3.Alice isn't here at the moment. She's GONE to the shop to get a newspaper
4.Tom has GONE out. He'll be back in about an hour
5. 'Are you going to the bank ? "No, I've already BEEN to the bank'

2. been 

3. gone

4. gone

5. been

Complete Bs sentences. Use the verb in brackets + just/already/yet (as sbown).

1. A: Would you something to eat?

B: No, thanks. I've just had lunch. (just/have)

2. A: Do you know where Julia is?

B: Yes, I --- her. (just/see) have just seen 

3. A: What time is David leaving?

B: He --- (already/leave) has already left

4. A: What's in the newspaper today?

B: I don't know. I --- (not/read/yet) haven't read yet

5. A: Is Ann coming to the cinema with us?

B: No, she --- the film. (already/see) has already seen 

6. A: Are your friends here yet? 

B: Yes, they --- (just/arrive)  have just arrived

7. A: What does Tim think about your plan?

B: I --- (not/tell/yet) haven't told yet

áp dụng công thức dãy số cách đều có quy luật bạn

Bạn có thể giải cho mình không vì mai mình học rồi !

( 2x - 1 )( x² - 6x + 15 ) > 0

Ta có : x² - 6x + 15 = ( x² - 6x + 9 ) + 6 = ( x - 3 )² + 6 ≥ 6 > 0 ∀ x

Để bpt > 0 => 2x - 1 > 0

                  => 2x > 1 

                  => x > 1/2

Vậy nghiệm của bất phương trình là x > 1/2

\(\frac{5x+4}{x^2+2x+7}< 0\)

Ta có : x² + 2x + 7 = ( x² + 2x + 1 ) + 6 = ( x + 1 )² + 6 ≥ 6 > 0 ∀ x

Để bpt < 0 => 5x + 4 < 0

                  => 5x < -4

                  => x < -4/5

Vậy nghiệm của bất phương trình là x < -4/5