Tìm x
x.x.x.x=16
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85:x=35 dư 15
=> 85=35.x+15
=> 35x=85-15
=> 35x=70
=> x=70:35
=> x=2
<=>3.3.3.3.3 = 3^5
<=>x.x.x.x=x^4
*** Ai k mk mk k lại cho !!!
1. \(\text{6 + 2.(x - 19) = 16}.\)
\(\Leftrightarrow2.\left(x-19\right)=10.\)
\(\Leftrightarrow x-19=5.\)
\(\Leftrightarrow x=24.\)
Vậy \(x=24.\)
2. \(\text{(-240) : x – 16 = 64}.\)
\(\Leftrightarrow\left(-240\right):x=80.\)
\(\Leftrightarrow x=-3.\)
Vậy \(x=-3.\)
3. \(2x^3=16.\)
\(\Leftrightarrow x^3=8.\)
\(\Leftrightarrow x=2.\)
Vậy \(x=2.\)
\(\left\{{}\begin{matrix}x-16=0\\3x-1=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=16\\x=\dfrac{1}{3}\end{matrix}\right.\)
\(S=\dfrac{x^3}{16\left(y+16\right)}+\dfrac{y^3}{16\left(x+16\right)}+\dfrac{2021}{2022}\)
\(\dfrac{x^3}{16\left(y+16\right)}+\dfrac{y+16}{100}+\dfrac{16}{80}\ge3\sqrt[3]{\dfrac{x^3\left(y+16\right).16}{16\left(y+16\right).100.80}}=\dfrac{3x}{20}\)
\(tương\) \(tự\Rightarrow\dfrac{y^3}{16\left(x+16\right)}\ge\dfrac{3y}{20}\)
\(\Rightarrow S\ge\dfrac{3x}{20}+\dfrac{3y}{20}-\left(\dfrac{x+16}{100}+\dfrac{y+16}{100}\right)-2.\dfrac{16}{80}+\dfrac{2021}{2022}=\dfrac{3x+3y}{20}-\dfrac{x+y+32}{100}-\dfrac{2}{5}+\dfrac{2021}{2022}=\dfrac{15x+15y-x-y-32}{100}-\dfrac{2}{5}+\dfrac{2021}{2022}=\dfrac{14\left(x+y\right)-32}{100}-\dfrac{2}{5}+\dfrac{2021}{2022}\)
\(xy=16\le\dfrac{\left(x+y\right)^2}{4}\Rightarrow x+y\ge8\Rightarrow S\ge\dfrac{14.8-32}{100}-\dfrac{2}{5}+\dfrac{2021}{2022}=\dfrac{2}{5}+\dfrac{2021}{2022}\)
\(\Rightarrow minS=\dfrac{2}{5}+\dfrac{2021}{2022}\Leftrightarrow x=y=4\)
\(\dfrac{x^3}{16\left(y+16\right)}+\dfrac{y+16}{100}+\dfrac{1}{5}\ge3\sqrt[3]{\dfrac{x^3\left(y+16\right)}{16.100.5\left(y+16\right)}}=\dfrac{3x}{20}\)
Tương tự: \(\dfrac{y^3}{16\left(x+16\right)}+\dfrac{x+16}{100}+\dfrac{1}{5}\ge\dfrac{3y}{20}\)
Cộng vế:
\(S+\dfrac{x+y+32}{100}+\dfrac{2}{5}\ge\dfrac{3\left(x+y\right)}{20}+\dfrac{2021}{2022}\)
\(S\ge\dfrac{9}{20}\left(x+y\right)-\dfrac{42}{25}+\dfrac{2021}{2022}\ge\dfrac{9}{20}.2\sqrt{xy}-\dfrac{42}{25}+\dfrac{2021}{2022}=...\)
Phương pháp giải:
- Muốn tìm số bị trừ ta lấy hiệu cộng với số trừ.
- Muốn tìm số trừ ta lấy số bị trừ trừ đi hiệu.
Lời giải chi tiết:
a) x – 9 = 16
x = 16 + 9
x = 25
b) x – 5 = 37
x = 37 + 5
x = 42
c) 31 – x = 16
x = 31 – 16
x = 15
Ta có : x . x . x . x =
<=> \(x^4=2^4\)
=> x = 2