Bạn nào có thể giúp mình câu toán này: 7×3^x-1-3^x+2=-540
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Đề trước đó:
(x-7)(x+1)-(x-3)^2=(3x-5)(3x+5)-(3x+1)^2+(x-2)^2-x
<=>x^2+x-7x-7-x^2+6x-9=9x^2-25-9x^2-6x-1+x^2-4x+4-x
<=>x^2-11x-6=0
<=>x^2-2x. 11/2 + 121/4-145/4=0
<=>(x-11/2)^2=145/4
<=>|x-11/2|=căn(145)/2
<=>x=[11+-căn(145)]/2
![](https://rs.olm.vn/images/avt/0.png?1311)
1.4x - 5(-3+x)=7
4x - 5(x-3) =7
4x - 5x + 15=7
-1x + 15=7
-1x =-8
=> x =8
2.5(x-3) - 2(x+6)=9
5x - 15 -2x -12=9
5x - 2x -15 - 12=9
5x - 2x=9 + 12 + 15
5x - 2x= 36
3x = 36
=> x = 12
3.4(x-1) - 3(x-2)=15
4x - 4 - 3x + 6=15
4x - 3x =15 - 6 + 4
4x - 3x = 13
=> x = 13
Nhớ mink nhoa pn
![](https://rs.olm.vn/images/avt/0.png?1311)
3/25 x ( 15/7 - 2/7 ) + 3/7 x 1/25
= 3/25 x 13/7 + 3/7 x 1/25
= (3 x 13/7 + 3/7 ) x 1/25
= 42/7 x 1/25
= 6 x 1/25
= 6/25
\(\dfrac{3}{25}\times\dfrac{15}{7}+\dfrac{3}{7}\times\dfrac{1}{25}-\dfrac{2}{7}\times\dfrac{3}{25}\)
\(=\dfrac{3}{25}\times\left(\dfrac{15}{7}-\dfrac{2}{7}\right)+\dfrac{3}{7}\times\dfrac{1}{25}\)
\(=\dfrac{3}{25}\times\dfrac{13}{7}+\dfrac{3}{7}\times\dfrac{1}{25}\)
\(=\dfrac{3\times13}{25\times7}+\dfrac{3\times1}{7\times25}\)
\(=\dfrac{39}{175}+\dfrac{3}{175}\)
\(=\dfrac{39+3}{175}\)
\(=\dfrac{42}{175}\)
\(=\dfrac{6}{25}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có :
\(7.3^{x-1}-3^{x+2}=-540\)
\(\Leftrightarrow\)\(7.3^x:3-3^x.3^2=-540\)
\(\Leftrightarrow\)\(\frac{7}{3}.3^x-9.3^x=-540\)
\(\Leftrightarrow\)\(3^x\left(\frac{7}{3}-9\right)=-540\)
\(\Leftrightarrow\)\(3^x.\frac{-20}{3}=-540\)
\(\Leftrightarrow\)\(3^x=\left(-540\right):\frac{-20}{3}\)
\(\Leftrightarrow\)\(3^x=81\)
\(\Leftrightarrow\)\(3^x=3^4\)
\(\Leftrightarrow\)\(x=4\)
Vậy \(x=4\)
lên sách giải lớp 7 mà nhìn bạn đỡ phải tốn thời gian