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a) \(\frac{1}{81}\): 3x = \(\frac{1}{729}\)
3x = \(\frac{1}{81}\): \(\frac{1}{729}\)
3x = 9
=> x = 2 ( vì 32 = 9 )
a) 3/7 + 4/9 + 4/7 + 5/9
= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )
= 7/7 + 9/9
= 1 + 1
= 2
b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5
= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5 ) + 5/5
= 2 + 2 + 2 + 2 + 1
= 2 x 4 + 1
= 8 +1
= 9
c) 1/8 + 1/12 + 3/8 + 5/12
= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)
= 4/8 + 6/12
= 1/2 + 1/2
= 2/4 = 1/2
mỏi tay rồi
d; (1 - \(\dfrac{1}{2}\)) x (1 - \(\dfrac{1}{3}\)) x (1 - \(\dfrac{1}{4}\)) x ... x ( 1 - \(\dfrac{1}{100}\))
= \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\) x \(\dfrac{3}{4}\) x \(\dfrac{3}{4}\) x ... x \(\dfrac{99}{100}\)
= \(\dfrac{1}{100}\)
7x = 49
7x = 72
=> x = 2
b) 2 . 4x + 1 = 129
2.4x = 129 - 1
2.4x = 128
4x = 128 : 2
4x = 64
4x = 43
=> x = 3
c) ( x - 5 )3 = 125
( x - 5 )3 = 53
x - 5 = 5
x = 5+5
x = 10
d) ( 4x - 1 )2 = 25 . 9
d) ( 4x - 1 )2 = 225
d) ( 4x - 1 )2 = 152
4x - 1 = 15
4x = 15 + 1
4x = 16
4x = 42
=> x = 2
a) 7x = 49
72 = 49
b) 2 . 4x + 1 = 129
2 . 4x = 129 - 1
2 . 4x = 128
4x = 128 : 2
4x = 64
=> 43
các câu còn lại làm giống như tìm x là đc
a) 1254:253= (53)3: (52)3=59:56=53
b) 414:528=414: 52.14=414:(52)14= 414:2514
c) 12n:22n=
1a) (x-2)(x+1)= 0
Suy ra \(\orbr{\begin{cases}x-2=0\\x+1=0\end{cases}}\)Suy ra \(\orbr{\begin{cases}x=2\\x=-1\end{cases}}\)
a) \(x\cdot25=5^3\)
\(x\cdot25=125\)
\(x=\frac{125}{25}\)
\(x=5\)
b) \(6^x:6^2=6^4\)
\(6^x=6^4\cdot6^2\)
\(6^x=6^6\)
\(x=6\)
c) \(3x=27\)
\(x=27:3\)
\(x=9\)
d) \(5^x+1=125\)
\(5^x=124\)
...
e) \(x\cdot36=6^8\)
\(x=6^8:6^2\)
\(x=6^6\)
\(x=46656\)
g) \(7^x+1:7^2=7^9\)
\(7^x=7^9-\frac{1}{7^2}\)
......
a, x = 125: 25 =5
b , 6 ^x =6^4 . 6^2
6^x =6^6
=> x =6
c, 3x = 27
=> 3x = 3 .9
=> x = 9 ( vì 3 =3 )
d, 5^x +1 =125
5 ^ x+1 =5^3
=>x +1 =3
=>x=2
e, x. 36 =6 ^8
x . 6^2 = 6^8
x = 6^8 : 6^2
x= 6^6
g , 7^x+1 : 7^2 = 7^9
7^x+1 = 7^2+9
7^x +1=7^ 11
=>x +1 =11
=> x =10
a)\(\dfrac{1}{3}^x=\dfrac{1}{729}\)
\(\dfrac{1}{3}^x=\dfrac{1}{3}^6\)
Suy ra x=6
vậy x=6
b)\(\left(\dfrac{1}{3}-\dfrac{1}{2}\right)^x=\dfrac{1}{36}\)
\(\left(-\dfrac{1}{6}\right)^x\)=\(\dfrac{1}{6}^2\)
Do đó x=2
Vậy x=2
c)\(\dfrac{25}{5}^x=\dfrac{1}{125}\)
\(5^x=5^{-3}\)
Suy ra x=-3
Vậy x=-3
d)\(7^{2n-\dfrac{1}{49}}=-343\)
\(-7^{2n-\dfrac{1}{49}}=-7^3\)
Do đó \(2n-\dfrac{1}{49}=3\)
2n=\(\dfrac{148}{49}\)
n=\(\dfrac{74}{49}\)
vậy n=\(\dfrac{74}{49}\)
chúc bạn học tốt ạ