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1.
a) ( 57 + 59 ) . ( 68 + 610 ) . ( 24 - 42 )
= ( 57 + 59 ) . ( 68 + 610 ) . 0
= 0
b) 9 < 3x < 27
32 < 3x < 33
2 < x < 3
Vậy 2 < x < 3
2.
a) xy - 2x = 0
x ( y - 2 ) = 0
\(\Rightarrow\orbr{\begin{cases}x=0\\y-2=0\end{cases}\Rightarrow\orbr{\begin{cases}x=3\\y=2\end{cases}}}\)
b) ( x- 4 ) . ( x - 3 ) = 0
\(\Rightarrow\orbr{\begin{cases}x-4=0\\x-3=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=4\\x=3\end{cases}}\)
c) Ta có : 3n+2 + 3n = 3n . 32 + 3n = 3n . ( 32 + 1 ) = 3n . 10 \(⋮\)10
Bài 1:
\(y^{10}=y\Rightarrow y^{10}-y=0\)
\(\Rightarrow y\left(y^9-1\right)=0\Rightarrow\orbr{\begin{cases}y=0\\y^9-1=0\Rightarrow y^9=1\Rightarrow y=1\end{cases}}\)
Bài 2:
\(a)16^x< 32^4\)
Ta có:\(16^x=\left(2^4\right)^x=2^{4x};32^4=\left(2^5\right)^4=2^{20}\)
\(\Rightarrow2^{4x}< 2^{20}\Rightarrow4x< 20=4.5\)mà \(x\inℕ\Rightarrow x\in\left\{0;1;2;3;4\right\}\)
\(b)9< 3^x< 81\)
\(\Rightarrow3^2< 3^x< 3^4\)
\(\Rightarrow2< x< 4\)mà \(x\inℕ\Rightarrow x=3\)
\(c)25< 5^x< 125\)
\(\Rightarrow5^2< 5^x< 5^3\)
\(\Rightarrow2< x< 3\)mà\(x\inℕ\Rightarrow\)không có giá trị x thõa mãn
y10 = y
<=> y10 - y = 0
<=> y(y - 1)(y2 + y + 1)(y6 + y3 + 1) = 0
=> y = 0, y = 1
\(\left(x-3\right)\left(x-12\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x-3=0\\x-12=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=3\\x=12\end{cases}}\)
\(\Rightarrow x\in\left\{3;12\right\}\)
\(\left(x^2-81\right)\left(x^2+9\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x^2-81=0\\x^2+9=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=9\\x\in\varnothing\end{cases}}\Leftrightarrow x=9\)
\(\Rightarrow x=9\)
\(\left(x-4\right)\left(x+2\right)< 0\)
\(\Rightarrow\hept{\begin{cases}x-4\\x+2\end{cases}}\)trái dấu
\(TH1:\hept{\begin{cases}x-4>0\\x+2< 0\end{cases}}\Leftrightarrow\hept{\begin{cases}x>4\\x< -2\end{cases}}\Leftrightarrow x\in\varnothing\)
\(TH2:\hept{\begin{cases}x-4< 0\\x+2>0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x< 4\\x>-2\end{cases}}\Leftrightarrow x\in\left\{-1;0;1;2;3\right\}\)
Vậy \(x\in\left\{-1;0;1;2;3\right\}\)
a) \(9< 3^x< 243\)
\(\Leftrightarrow3^2< 3^x< 3^5\)
\(\Rightarrow x\in\left\{3;4\right\}\)
b) Sửa đề: \(3^4.3^x\div9=27\)
\(\Leftrightarrow3^{x+4}=3\)
\(\Rightarrow x+4=1\)
\(\Rightarrow x=-3\)
c) \(3^x\div3^2=243\)
\(\Leftrightarrow3^{x-2}=3^5\)
\(\Rightarrow x-2=5\)
\(\Rightarrow x=7\)
d) \(25< 5^x< 3125\)
\(\Leftrightarrow5^2< 5^x< 5^5\)
\(\Rightarrow x\in\left\{3;4\right\}\)
e) \(2^x-64=2^6\)
\(\Leftrightarrow2^x=64+64=128\)
\(\Leftrightarrow2^x=2^7\)
\(\Rightarrow x=7\)
f) \(2^x\div16=128\)
\(\Leftrightarrow2^x=2^7.2^4\)
\(\Leftrightarrow2^x=2^{11}\)
\(\Rightarrow x=11\)
1.
a. 9 < \(^{3^y}\)< 81
9=3\(^{^2}\)
81=3\(^{^4}\)
\(\Rightarrow\)y=3 vì \(3^2< 3^3< 3^4\)
b.25\(\le\)5\(^{^y}\)\(\le\)125
25=5\(^{^2}\)
125=5\(^{^3}\)
\(\Rightarrow\)y=2 và 3 vì 5\(^{^2}\)\(\le\)5\(^{^2}\)(5\(^{^3}\))\(\le\)5\(^{^3}\)
c.
16\(\ge\)4\(^{^y}\)\(\ge\)1024
16=4\(^{^2}\)
1024=4\(^{^5}\)
\(\Rightarrow\)y=2,3,4,5 vì 4\(^{^2}\)\(\ge\)4\(^{^2\left(4^3;4^4;4^5\right)}\)
\(^{^2}\)
\(\Rightarrow\)
2.
a.3x\(^{2^y}\)=48
\(^{2^y}\)=48:3
\(^{2^y}\)=16
\(\Rightarrow\)y=4 vì \(^{2^4}\)=16
b.5x\(y^7\)=640
\(y^7\)=640:5
\(y^7\)=128
\(\Rightarrow\)y=2 vì \(2^7\)=128
c.\(y^{100}\)=\(y^2\)
\(\Rightarrow\)y=1 vì:
\(1^{100}\)=1
\(1^2\)=1
d.(y-3)\(^{^5}\)=243
\(\Rightarrow\)y-3=3 vì 3\(^{^5}\)=243
y=3+3
y=6
e.(2y+1)\(^{^3}\)=125
\(\Rightarrow\)2y+1=5 vì 5\(^{^3}\)=125
2y=5-1=4
y=4:2=2
i.2\(^{^{y+3}}\)+2\(^{^y}\)=288
2\(^{^y}\).2\(^{^3}\)+2\(^{^y}\)=288
2\(^{^y}\).2\(^{^3}\)=288-2\(^{^y}\)
2\(^{^y}\).8=288-2\(^{^y}\)
8=(288-2\(^{^y}\)):2\(^{^y}\)
8=288:2\(^{^y}\)-2\(^{^y}\):2\(^{^y}\)
8=288:2\(^{^y}\)-1
288:2\(^{^y}\)=8+1=9
2\(^{^y}\)=288:9=32
\(\Rightarrow\)y=5 vì 2\(^{^5}\)=32