Tìm a biết : aaaaa /a x37 - 4866 x (2x3)
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
aaaaaa : (a x 37) – 4866 : (2 x 3)
= aaaaaa : a : 37 – 4866 : 6
= 111111 : 37 – 811
= 3003 – 811
= 2192
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
f'(x)=2*3x^2+3*2*(a+2)*x+6a^2
=6x^2+6x(a+2)+6a^2
Δ=(6a+12)^2-4*6*6a^2
=36a^2+144a+144-144a^2
=-108a^2+144a+144
f'(x)>0 với mọi x
=>-108a^2+144a+144<0
=>a<-2/3; a>2
f'(-1)=6
=>6*(-1)^2+6*(-1)*(a+2)+6a^2=6
=>6a^2+6-6a-12=6
=>6a^2-6a-12=0
=>a^2-a-2=0
=>a=2(loại) hoặc a=-1(nhận)
![](https://rs.olm.vn/images/avt/0.png?1311)
=1/2-1/3+1/3-1/4+.......+1/a-1/a+1=49/100
1/2-1/a+1=49/100
1/a+1 = 1/2-49/100
1/a+1=1/100
a+1=100
a=99
=1/2-1/3+1/3-1/4+.......+1/a-1/a+1=49/100
1/2-1/a+1=49/100
1/a+1 = 1/2-49/100
1/a+1=1/100
a+1=100
a=99
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^4+2x^3-4x=4\)
\(\Leftrightarrow\left(x^2-2\right)\left(x^2+2\right)+2x\left(x^2-2\right)=0\)
\(\Leftrightarrow x^2-2=0\)
hay \(x\in\left\{\sqrt{2};-\sqrt{2}\right\}\)
\(\Rightarrow x^4+2x^3-4x-4=0\\ \Rightarrow x^4-2x^2+2x^3-4x+2x^2-4=0\\ \Rightarrow\left(x^2-2\right)\left(x^2+2x+2\right)=0\\ \Rightarrow\left[{}\begin{matrix}x^2=2\\\left(x+1\right)^2+1=0\left(vô.lí\right)\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\sqrt{2}\\x=-\sqrt{2}\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
aaaaaa : (a x 37) - 4866 : (2 x 3)
= aaaaaa : a : 37 - 4866 : 6
= 111111 : 37 - 811
= 3003 - 811
= 2192
![](https://rs.olm.vn/images/avt/0.png?1311)
haiz khó thế