cho a,b>0 thỏa mãn a+b=a^3+b^3=a^2+b^2tính a^2012⋅b^2013
Cho a,b,c >0 thỏa mãn abc=1. Tìm min A=\(\dfrac{a^{2013}+b^{2013}+c^{2013}}{a^{2012}+b^{2012}+c^{2012}}\)
\(a^{2012}+b^{2012}+c^{2012}\ge3\sqrt[3]{\left(abc\right)^{2012}}=3\)
\(\Rightarrow\dfrac{1}{a^{2012}+b^{2012}+c^{2012}}\le\dfrac{1}{3}\)
\(\Rightarrow-\dfrac{1}{a^{2012}+b^{2012}+c^{2012}}\ge-\dfrac{1}{3}\)
Lại có:
\(a^{2013}+a^{2013}+...+a^{2013}\left(\text{2012 số hạng}\right)+1\ge2013\sqrt[2013]{\left(a^{2013}\right)^{2012}}=2013.a^{2012}\)
\(\Rightarrow2012.a^{2013}+1\ge2013.a^{2012}\)
Tương tự: \(2012.b^{2013}+1\ge2013.b^{2012}\) ; \(2012.c^{2013}+1\ge2013.c^{2012}\)
Cộng vế với vế:
\(\Rightarrow a^{2013}+b^{2013}+c^{2013}\ge\dfrac{2013\left(a^{2012}+b^{2012}+c^{2012}\right)-3}{2012}\)
\(\Rightarrow A\ge\dfrac{2013\left(a^{2012}+b^{2012}+c^{2012}\right)-3}{2012\left(a^{2012}+b^{2012}+c^{2012}\right)}=\dfrac{2013}{2012}-\dfrac{3}{2012}.\dfrac{1}{a^{2012}+b^{2012}+c^{2012}}\ge\dfrac{2013}{2012}-\dfrac{3}{2012}.\dfrac{1}{3}=1\)
\(A_{min}=1\) khi \(a=b=c=1\)
Cho các số dương a và b thỏa mãn :a+b=a^2+b^2=a^3+b^3 . Tính a^2012 *b^2013
cho a,b khác 0 thỏa mãn a^2014 + b^2014 = a^2013 + b^2013 = a^2012 + b^2012
chứng minh rằng : a^2014 + b^2014 = a^2010 + b^2010
Đề \(\Rightarrow a^{2014}+b^{2014}-2\left(a^{2013}+b^{2013}\right)+a^{2012}+b^{2012}=0\)
\(\Leftrightarrow a^{2012}\left(a^2-2a+1\right)+b^{2012}\left(b^2-2b+1\right)=0\)
\(\Leftrightarrow a^{2012}\left(a-1\right)^2+b^{2012}\left(b-1\right)^2=0\)
\(\Leftrightarrow\left(a=0\text{ hoặc }a=1\right)\text{ và }\left(b=0\text{ hoặc }b=1\right)\)
\(+a=0\text{ hoặc }a=1\text{ thì }a^{2014}=a^{2010}\)
\(+b=0\text{ hoặc }b=1\text{ thì }b^{2014}=b^{2010}\)
Suy ra \(a^{2014}+b^{2014}=a^{2010}+b^{2010}\)
Cho a , b , c thỏa mãn \(a^2+b^2+c^2=a^3+b^3+c^3=1\) Tính \(P=a^{2012}+b^{2013}+c^{2014}\)
Ta có: \(a^2+b^2+c^2=1\)
\(\Rightarrow\left\{{}\begin{matrix}\left|a\right|\le1\\\left|b\right|\le1\\\left|c\right|\le1\end{matrix}\right.\)
Ta lại có:
\(a^3+b^3+c^3=a^2+b^2+c^2\)
\(\Leftrightarrow a^2\left(1-a\right)+b^2\left(1-b\right)+c^2\left(1-c\right)=0\)
Vì \(\left\{{}\begin{matrix}1-a\ge0\\1-b\ge0\\1-c\ge0\end{matrix}\right.\)
\(\Rightarrow a^2\left(1-a\right)+b^2\left(1-b\right)+c^2\left(1-c\right)\ge0\)
Dấu = xảy ra khi: \(\left(a,b,c\right)=\left(1,0,0;0,1,0;0,0,1\right)\)
\(\Rightarrow S=1\)
cho a,b>0 thỏa mãn \(a+b=a^3+b^3=a^2+b^2\)tính \(a^{2012}\cdot b^{2013}\)
a+b=a3+b3=a2+b2 <=> a và b =1 hoặc a và b=0
Mà a,b > 0 => a+b >0 => a=b=1
=> a2012 + b2013 = 1+ 1= 2
Vậy: ...........................
Cho 2 số dương a, b thỏa mãn: a2012 + b2012 = a2013 + b2013 = a2014 + b2014.
Hãy tính M = 20a + 11b + 2013
ta có \(a^{2012}+b^{2012}=a^{2013}+b^{2013}\)
\(\Rightarrow a^{2012}-a^{2013}+b^{2012}_{ }-b^{2013}=0\)
\(\Rightarrow a^{2012}\left(1-a\right)+b^{2012}\left(1-b\right)=0\)\(\left(1\right)\)
tương tự \(a^{2013}+b^{2013}=a^{2014}+b^{2014}\)
\(\Leftrightarrow a^{2013}\left(1-a\right)+b^{2013}\left(1-b\right)=0\)\(\left(2\right)\)
trừ (1) cho (2)
ta có \(\left(a^{2012}-a^{2013}\right)\left(1-a\right)\)\(+\left(b^{2012}-b^{2013}\right)\left(1-b\right)=0\)
\(\Leftrightarrow a^{2012}\left(1-a\right)^2+b^{2012}\left(1-b\right)^2=0\)
mà\(a^{2012}\left(1-a\right)^2\ge0;b^{2012}\left(1-b\right)^2\ge0\)
\(\Rightarrow a=1;b=1\)
\(\Rightarrow M=20\times1+11\times1+2013=2044\)
lay cai dau tru cai thu 2
xong lay cai thu 2 tru cai thu 3
xong lay ket qua dau tim dc tru ket qua sau la tim dc a=b=1
roi thay vao tinh M la xong
Ta có: \(a^{2012}+b^{2012}=a^{2013}+b^{2012}=a^{2014}+b^{2014}\)
\(\Rightarrow a^{2012}+b^{2012}-2\left(a^{2013}+b^{2013}\right)+a^{2014}+b^{2014}=0\)
\(\Rightarrow a^{2012}+b^{2012}-2\left(a^{2013}+b^{2013}\right)+a^{2014}+b^{2014}=0\)
\(\Leftrightarrow\left(a^{1006}-a^{1007}\right)^2+\left(b^{1006}-b^{1007}\right)=0\)
Từ đó ta có 2 TH
\(\hept{\begin{cases}a^{1006}-a^{1007}=0\\b^{1006}-b^{1007}=0\end{cases}\hept{\begin{cases}a=0;a=1\\b=0;b=1\end{cases}}}\)
Vậy P=20.0+11.0+2013=2013
P=20.1+11.0+2013=2033
P=20.0+11.1+2013=2024
Ch 2 số dương a , b thỏa mãn : a^2012 + b^2012 = a^2013 + b^2013 = a^2014 + b^2014 . Tính : P = 20a + 11b + 2013
cho a ,b,c thảo mãn a^2012+b^2012+c^2012=a^2013+b^2013+c^2013=1 tính B = a^2011+b^2012+c^2013
Bài 1: Tìm \(\overline{abcde}\), biết
1) \(\sqrt{\overline{abcde}}\) = 5e + 1
2) \(\sqrt{\overline{abcde}}\) = \(\left(ab\right)^3\)
Bài 2: Cho a, b>0: \(a^{2012}\)+ \(b^{2012}\) = \(a^{2013}\)+\(b^{2013}\)=\(a^{2014}\)+\(b^{2014}\)
Bài 3: Tìm a, b, c: a.( a + b + c ) = \(-\dfrac{1}{24}\)
c.( a + b + c ) = \(-\dfrac{1}{72}\)
b.( a + b + c ) = \(\dfrac{1}{16}\)
(cứu mih với ạ uhuhuhu)
Bài 3.
\(\left\{{}\begin{matrix}a\left(a+b+c\right)=-\dfrac{1}{24}\left(1\right)\\c\left(a+b+c\right)=-\dfrac{1}{72}\left(2\right)\\b\left(a+b+c\right)=\dfrac{1}{16}\left(3\right)\end{matrix}\right.\)
Dễ thấy \(a,b,c\ne0\Rightarrow a+b+c\ne0\)
Chia (1) cho (2), ta được \(\dfrac{a}{c}=3\Rightarrow a=3c\left(4\right)\)
Chia (2) cho (3) ta được: \(\dfrac{c}{b}=-\dfrac{2}{9}\Rightarrow b=-\dfrac{9}{2}c\left(5\right)\).
Thay (4), (5) vào (2), ta được: \(-\dfrac{1}{2}c^2=-\dfrac{1}{72}\)
\(\Rightarrow c=\pm\dfrac{1}{6}\).
Với \(c=\dfrac{1}{6}\Rightarrow\left\{{}\begin{matrix}a=3c=\dfrac{1}{2}\\b=-\dfrac{9}{2}c=-\dfrac{3}{4}\end{matrix}\right.\)
Với \(c=-\dfrac{1}{6}\Rightarrow\left\{{}\begin{matrix}a=3c=-\dfrac{1}{2}\\b=-\dfrac{9}{2}c=\dfrac{3}{4}\end{matrix}\right.\)
Vậy: \(\left(a;b;c\right)=\left\{\left(\dfrac{1}{2};-\dfrac{3}{4};\dfrac{1}{6}\right);\left(-\dfrac{1}{2};\dfrac{3}{4};-\dfrac{1}{6}\right)\right\}\)