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Bài 3:
a, Đặt \(A=\left|2x-\frac{1}{5}\right|+2017\)
Để A đạt GTNN thì \(\left|2x-\frac{1}{5}\right|\)đạt GTNN
Mà \(\left|2x-\frac{1}{5}\right|\ge0\)
Do đó \(\left|2x-\frac{1}{5}\right|=0\)thì A đạt GTNN tức là A = 0 + 2017 = 2017 khi
\(2x-\frac{1}{5}=0=>2x=0+\frac{1}{5}=\frac{1}{5}=>x=\frac{1}{5}.\frac{1}{2}=\frac{1}{10}\)
b, Đặt \(B=\left|x+\frac{1}{2}\right|+\left|x+\frac{1}{3}\right|+\left|x+\frac{1}{4}\right|\)
Ta thấy \(\frac{1}{2}>\frac{1}{3}>\frac{1}{4}=>x+\frac{1}{2}>x+\frac{1}{3}>x+\frac{1}{4}\)
Do đó để B đạt GTNN thì \(x+\frac{1}{2}\)đạt GTNN
mà \(x+\frac{1}{2}\ge0\)
Từ 2 điều trên => \(x+\frac{1}{2}=0=>x=-\frac{1}{2}\)
Khi đó \(x+\frac{1}{3}=-\frac{1}{2}+\frac{1}{3}=-\frac{1}{6}\)
và \(x+\frac{1}{4}=-\frac{1}{2}+\frac{1}{4}=-\frac{1}{4}\)
Vậy GTNN của \(B=\left|0\right|+\left|-\frac{1}{6}\right|+\left|-\frac{1}{4}\right|=0+\frac{1}{6}+\frac{1}{4}=\frac{10}{24}\)khi x = -1/2
Phần b này thì mình không chắc lắm bạn tự xem lại nhé
Bài 1:
\(M=\frac{2017}{11-x}\)đạt GTLN <=> 11 - x đạt GTNN và 11 - x > 0 (nếu không thì M đạt giá trị âm (vô lí))
=> 11 - x = 1
=> x = 10
Vậy x = 10 thì M đạt GTLN tức là bằng \(\frac{2017}{1}=2017\)
Xét hiệu
(x+y+z)3-x3-y3-z3=[(x+y)+z]3-x3-y3-z3
=(x+y)3+3(x+y)2z+3(x+y)z2+z3-x3-y3-z3
=(x+y)3+3z(x+y)(x+y+z)+z3-x3-y3-z3
=x3+3x2y+3xy2+y3+3z(x+y)(x+y+z)+z3-x3-y3-z3
=(x3-x3)+(y3-y3)+(z3-z3)+3xy(x+y)+3z(x+y)(x+y+z)
=3(x+y)(xy+yz+xz+z2)
=3(x+y)[y(x+z)+z(x+z)]
=3(x+y)(x+z)(y+z
=>(x+y+z)3-x3-y3-z3=3(x+y)(y+z)(z+x)
=>(x+y+z)3=3(x+y)(y+z)(z+x)+x3+y3+z3
=> DPCM
ta có: \(\left(x+y+z\right)^3-x^3-y^3-z^3\)\(=\left[\left(x+y+z\right)^3-x^3\right]-\left(y^3+z^3\right)\)
\(=\left(x+y+z-x\right)\left[\left(x+y+z\right)^2+\left(x+y+z\right)x+x^2\right]-\left(y+z\right)\left(y^2-yz+z^2\right)\)
\(=\left(y+z\right)\left(x^2+y^2+z^2+2xy+2xz+2yz+x^2+xy+xz+x^2-y^2+yz-z^2\right)\)
\(=\left(y+z\right)\left(3x^2+3xy+3xz+3yz\right)\)
\(=\left(y+z\right)\left[3x\left(x+y\right)+3z\left(x+y\right)\right]\)
\(=\left(y+z\right)\left(x+y\right)\left(3x+3z\right)\)
\(=3\left(y+z\right)\left(x+y\right)\left(x+z\right)\)(đpcm)
a. 5 : x = x : 125
x=125:5
x=25
b. 2x + 3 = 4 + 3x
2x-3x=4-3
-x=1
x=-1
\(\frac{\left(\frac{2}{3}\right)^3.\left(\frac{-3}{4}\right)^2.\left(-1\right)^{2003}}{\left(\frac{2}{5}\right)^2.\left(\frac{-5}{12}\right)^3}\)=\(\frac{\frac{8}{27}.\frac{9}{16}.-1}{\frac{4}{25}.\frac{-125}{1728}}\)=\(\frac{\frac{-1}{6}}{-\frac{5}{432}}\)=\(\frac{-1}{6}:\frac{-5}{432}=\frac{-1}{6}.-\frac{432}{5}=\frac{72}{5}\)
Bài này dễ mà bn
\(b.\)ghi lại đề nha bn
\(=\frac{2.2306}{1+\frac{1}{\frac{2.3}{2}}+\frac{1}{\frac{3.4}{2}}+...+\frac{1}{\frac{230.231}{2}}}\)
\(=\frac{2.2306}{1+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{230.231}}\)
\(=\frac{2.2306}{1+2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{230.231}\right)}\)
\(=\frac{2.2306}{1+2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{230}-\frac{1}{231}\right)}\)
\(=\frac{2.2306}{1+2.\left(\frac{1}{2}-\frac{1}{231}\right)}\)
\(=\frac{2.2306}{1+1-\frac{2}{231}}\)
\(=\frac{2.2306}{2-\frac{2}{231}}\)
\(=\frac{2.2306}{2\left(1-\frac{1}{231}\right)}\)
\(=\frac{2306}{1-\frac{1}{231}}\)
mình nha bn thanks nhìu <3
a) \(\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2017}}{\frac{2016}{1}+\frac{2015}{2}+...+\frac{1}{2016}}\)
\(=\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2017}}{\left(\frac{2015}{2}+1\right)+...+\left(\frac{1}{2016}+1\right)+1}\)
\(=\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2017}}{\frac{2017}{2}+...+\frac{2017}{2016}+\frac{2017}{2017}}\)
\(=\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2017}}{2017.\left(\frac{1}{2}+...+\frac{1}{2016}+\frac{1}{2017}\right)}\)
\(=\frac{1}{2017}\)