cho a,b,c la cac so thuc duong. chung minh rang 2a/(b+c)+2b/(c+a)+2c/(a+b)>=((a-b)^2+(b-c)^2+(c-a)^2)/(a+b+c)^2
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cho a , b, c la cac so thuc duong thoa man he thuc a+b+c=6abc
Chung minh rang \(\dfrac{bc}{a^3\left(c+2b\right)}+\dfrac{ac}{b^3\left(a+2c\right)}+\dfrac{ab}{c^3\left(b+2a\right)}\ge2\)
Cho a,b,c la cac so thuc duong:Tim GTLN cua bieu thuc P= (a^2b+b^2c+c^2a);(a^2+b^2+c^2)- 1:3(a^2+b^2+c^2)
Cho a,b,c là những số dương abc=1. Tìm GTLN của P\(=\frac{1}{a^2+2b^2+3}+\frac{1}{b^2+2c^2+3}+\frac{1}{c^2+2a^2+3}\)
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\(\frac{1}{a^2+2b^2+3}=\frac{1}{\left(a^2+b^2\right)+b^2+1+2}\le\frac{1}{2}\left(\frac{1}{ab+b+1}\right)\)
tương tự với những cái còn lại, ta sẽ đc 1 bài quen thuộc
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cho 3 so duong a,b,c thoa man a+b+c=1/abc chung minh rang can ((1+b^2c^2)(1+a^2c^2)/c^2+a^2b^2c^2)=a+b
cho x,y,z la cac so nguyen duong va x+y+z la so le, cac so thuc a,b,c thoa man (a-b)/x=(b-c)/y=(a-c)/z. chung minh rang a=b=c
Cho a,b.c la cac so duong va abc = 1
Chung minh rang \(\frac{1}{a^2+2b^2+3}+\frac{1}{b^2+2c^2+3}+\frac{1}{c^2+2a^2+3}\le\frac{1}{2}\)
1. Cho a,b la 2 so duong thoa a+b<=1.chung minh rang \(6b+\frac{1}{3a}+\frac{4}{b}\ge11\).
2. cho a,b,c la cac so nguyen duong sao cho (a-b).(a-c).(b-c)=a+b+c
a. chung minh rang a+b+c chia het cho 2
b. Tim gia tri nho nhat cua M=a+b+c
Cho a,b,c la cac so duong .Chung minh rang:
a^2016+b^2016+c^2016 >hoac=(b+c).a^2015/2+(c+a).b^2015/2+(a+b).c^2015/2
cho ti le thuc a/b = c/d ,chung to rang a,3a + 2b / a = 3c + 2d / c ; b, 2a - 3b/ b = 2c - 3d / b ; c, a/ a-2b = c/c-2d giup minh voi dang can gap
Đặt a/b=c/d=k
=>a=bk; c=dk
a: \(\dfrac{3a+2b}{a}=\dfrac{3bk+2b}{bk}=\dfrac{3k+2}{k}\)
\(\dfrac{3c+2d}{c}=\dfrac{3dk+2d}{dk}=\dfrac{3k+2}{k}\)
Do đó: \(\dfrac{3a+2b}{a}=\dfrac{3c+2d}{c}\)
b: \(\dfrac{2a-3b}{b}=\dfrac{2bk-3b}{b}=2k-3\)
\(\dfrac{2c-3d}{d}=\dfrac{2dk-3d}{d}=2k-3\)
Do đó: \(\dfrac{2a-3b}{b}=\dfrac{2c-3d}{d}\)
c: \(\dfrac{a}{a-2b}=\dfrac{bk}{bk-2b}=\dfrac{k}{k-2}\)
\(\dfrac{c}{c-2d}=\dfrac{dk}{dk-2d}=\dfrac{k}{k-2}\)
Do đó: \(\dfrac{a}{a-2b}=\dfrac{c}{c-2d}\)
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cho 2 p/s a/b vs c/d (a,b,c,d la cac so nguyen duong ) chung minh rang neu a/b < c/d thi b/a > d/c