Tìm x,y:
\(\dfrac{2x.37,7}{56x+16y}\)= 0,95
Tìm x và y biết 56x+16y=160
cho hỏi làm sao mà 56x/16y = 72.144%/27.856% mà ⇒ x/y = 3/4 vậy ạ?
\(\dfrac{56x}{16y}= \dfrac{72,144\%}{27,856\%}\\ \Rightarrow\dfrac{x}{y} = \dfrac{72,144\%}{27,856\%} : \dfrac{56}{16} = 0,75 = \dfrac{3}{4}\)
Gọi công thức E là FexOy
=>M(FexOy)=56x+16y(g/mol)
có %Oxi=16y=15,6x+4,46y<=>11,54y=16x=>11,54y=15,6x=>xy=11,5415,6≈3/4
Tính tỉ lệ x:y
\(\dfrac{0,6}{3x-2y}.\left(56x+16y\right)+\dfrac{0,3}{3x-2y}.40=151,2\)
Tìm x, y biết: \(\frac{2.x.56}{2,24}=\frac{2.\left(56x+16y\right)}{3,2}\).
\(\frac{2x.56}{2,24}=\frac{2\left(56x+16y\right)}{3,2}\)
\(\Leftrightarrow\frac{112x}{2,24}=\frac{56x+16y}{1,6}\)
\(\Leftrightarrow50x=\frac{56x+16y}{1,6}\)
\(\Leftrightarrow80x=56x+16y\)
\(\Leftrightarrow24x=16y\)
\(\Leftrightarrow\frac{x}{y}=\frac{16}{24}=\frac{2}{3}\)
\(\Leftrightarrow x=2;y=3\)
Vậy .....................
1. Tìm max và min
a) \(A=\sqrt{x-3}+\sqrt{7-x}\)
b) \(B=\dfrac{3+8x^2+12x^4}{\left(1+2x^2\right)^2}\)
2. Cho \(36x^2+16y^2=9\)
\(CM:\dfrac{15}{4}\text{≤}y-2x+5\text{≤}\dfrac{25}{4}\)
a) ĐKXĐ : \(3\le x\le7\)
Ta có \(A=1.\sqrt{x-3}+1.\sqrt{7-x}\)
\(\le\sqrt{\left(1+1\right)\left(x-3+7-x\right)}=\sqrt{8}\)(BĐT Bunyacovski)
Dấu "=" xảy ra <=> \(\dfrac{1}{\sqrt{x-3}}=\dfrac{1}{\sqrt{7-x}}\Leftrightarrow x=5\)
\(1,\\ a,A\le\sqrt{\left(x-3+7-x\right)\left(1+1\right)}=\sqrt{8}=2\sqrt{2}\\ A^2=4+2\sqrt{\left(x-3\right)\left(7-x\right)}\ge4\Leftrightarrow A\ge2\\ \Leftrightarrow2\le A\le2\sqrt{2}\\ \left\{{}\begin{matrix}A_{min}\Leftrightarrow\left(x-3\right)\left(7-x\right)=0\Leftrightarrow...\\A_{max}\Leftrightarrow x-3=7-x\Leftrightarrow x=5\end{matrix}\right.\)
\(B=\dfrac{\dfrac{5}{2}\left(4x^4+4x^2+1\right)+2\left(x^4-x^2+\dfrac{1}{4}\right)}{\left(2x^2+1\right)^2}\\ B=\dfrac{\dfrac{5}{2}\left(2x^2+1\right)^2+2\left(x^2-\dfrac{1}{2}\right)^2}{\left(2x^2+1\right)^2}=\dfrac{5}{2}+\dfrac{2\left(x^2-\dfrac{1}{2}\right)^2}{\left(2x^2+1\right)^2}\ge\dfrac{5}{2}\)
\(B=\dfrac{3\left(4x^4+4x^2+1\right)-4x^2}{\left(1+2x^2\right)^2}=\dfrac{3\left(1+2x^2\right)^2-4x^2}{\left(1+2x^2\right)^2}=3-\dfrac{4x^2}{\left(1+2x^2\right)^2}\)
Vì \(-\dfrac{4x^2}{\left(1+2x^2\right)^2}\le0\Leftrightarrow B\le3\)
\(\Leftrightarrow\left\{{}\begin{matrix}B_{min}\Leftrightarrow x^2=\dfrac{1}{2}\Leftrightarrow x=\pm\dfrac{1}{\sqrt{2}}\\B_{max}\Leftrightarrow x=0\end{matrix}\right.\)
\(2,\)
Ta có \(\left(y-2x\right)^2=\left(-2x+y\right)^2=\left[\dfrac{1}{3}\left(-6x\right)+\dfrac{1}{4}\left(4y\right)\right]^2\)
\(\Leftrightarrow\left(y-2x\right)^2\le\left[\left(\dfrac{1}{3}\right)^2+\left(\dfrac{1}{4}\right)^2\right]\left[\left(-6x\right)^2+\left(4y\right)^2\right]=\dfrac{5^2}{3^2\cdot4^2}\left(36x^2+16y^2\right)=\dfrac{5^2}{4^2}\\ \Leftrightarrow\left|y-2x\right|\le\dfrac{5}{4}\\ \Leftrightarrow-\dfrac{5}{4}\le y-2x\le\dfrac{5}{4}\\ \Leftrightarrow\dfrac{15}{4}\le y-2x+5\le\dfrac{25}{4}\)
\(Max\Leftrightarrow\left\{{}\begin{matrix}-18x=16y\\y-2x=\dfrac{5}{4}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-\dfrac{2}{5}\\y=\dfrac{9}{20}\end{matrix}\right.\\ Min\Leftrightarrow\left\{{}\begin{matrix}-18x=16y\\y-2x=-\dfrac{5}{4}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{2}{5}\\y=-\dfrac{9}{20}\end{matrix}\right.\)
có bạn nào giúp mình trả lời câu hỏi này nhanh hay chỉ mình cách giải cũng được:
5,6 +b(56x + 16y)= 12,8
7,2 +b(56x+16y) = 16
xin cảm ơn :))
Giải gấp PT này vs.
\(\frac{16}{56x+16y}=\frac{32,5x}{56+\frac{71y}{x}}\)
Không cần ra kết quả x,y bằng bao nhiêu.Ra tỉ lệ x,y là Ok rồi. Thanks trước.
cho x+3y=5 tìm GTNN của biểu thức A=x^2+y^2+16y+2x
Ta có: x+3y=5 => x=5-3y
Lại có: A=x^2+y^2+16y+2x
=> A=(5-3y)^2+y^2+16y+2(5-3y)=25-30y+9y^2+y^2+16y+10-6y
=35+10y^2-20y=10(y^2-2y+1)+25=10(y-1)^2+25
Ta thấy: 10(y-1)^2 luôn lớn hơn hoặc bằng 0 với mọi y
=> A luôn lớn hơn hoặc bằng 25 với mọi y
Dấu "=" xảy ra <=> 10(y-1)^2=0 <=> y=1 => x=5-3*1=2
Vậy minA=25 <=> x=2; y=1
Tìm x, y, z biết: 7/3x = 2/16y = 19/6z ; 2x-y-z=-6
nhanhhhhhhhhhhh