\(6,\\ a,P=9\left(x^2-2\cdot\dfrac{1}{9}x+\dfrac{1}{81}\right)+\dfrac{26}{9}=9\left(x-\dfrac{1}{9}\right)^2+\dfrac{26}{9}\ge\dfrac{26}{9}\\ P_{min}=\dfrac{26}{9}\Leftrightarrow x-\dfrac{1}{9}=0\Leftrightarrow x=\dfrac{1}{9}\\ b,Q=3\left(x^2-x+\dfrac{1}{4}\right)+\dfrac{1}{4}=3\left(x-\dfrac{1}{2}\right)^2+\dfrac{1}{4}\ge\dfrac{1}{4}\\ Q_{min}=\dfrac{1}{4}\Leftrightarrow x-\dfrac{1}{2}=0\Leftrightarrow x=\dfrac{1}{2}\\ c,R=\left(x^2-2xy+y^2\right)+x^2+1=\left(x-y\right)^2+x^2+1\ge1\\ R_{min}=1\Leftrightarrow\left\{{}\begin{matrix}x-y=0\\x=0\end{matrix}\right.\Leftrightarrow x=y=0\)

Câu 2:

\(1.f\left(x\right)=2x^3+x^2-3x+9.\\ g\left(x\right)=-2x^3-x^2+3.\)

Câu 3:

1. Ta có: \(AB=AC\) (\(\Delta ABC\) cân).

Mà \(AC=IC\left(gt\right). \)

\(\Rightarrow AB=IC.\)

Ta có: \(\widehat{ABC}=\widehat{ACB}\) (\(\Delta ABC\) cân).

Mà \(\widehat{ACB}=\widehat{ICE}\) (đối đỉnh).

\(\Rightarrow\widehat{ABC}=\widehat{ICE}.\)

Hay \(\widehat{ABD}=\widehat{ICE}.\)

Xét \(\Delta ABD\) và \(\Delta ICE:\)

BD = CE (gt).

\(\widehat{ABD}=\widehat{ICE}\left(cmt\right).\)

AB = IC (cmt).

\(\Rightarrow\Delta ABD=\Delta ICE\left(c-g-c\right).\)

2. Xét \(\Delta BDM\) và \(\Delta CEN:\)

\(\widehat{MBD}=\widehat{NCE}\left(\widehat{ABD}=\widehat{ICE}\right).\)

\(BD=CE\left(gt\right).\)

\(\widehat{BDM}=\widehat{CEN}\left(=90^o\right).\)

\(\Rightarrow\Delta BDM=\Delta CEN\left(g-c-g\right).\)

\(\Rightarrow BM=CN\) (2 cạnh tương ứng).

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      A  =          \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) +    \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\)+.....+  \(\dfrac{1}{134}\)+ \(\dfrac{1}{268}\)

A \(\times\) 2 =  1  +  \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\)   + \(\dfrac{1}{8}\)  + \(\dfrac{1}{16}\) + \(\dfrac{1}{32}\) +.....+ \(\dfrac{1}{134}\)

A \(\times\) 2 - A = 1 - \(\dfrac{1}{268}\)

A \(\times\) ( 2  - 1) = \(\dfrac{267}{268}\)

A = \(\dfrac{267}{268}\)

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x3 + 3x = 12.11

=> x(3+3) = 12.11

=> 6x = 12.11

=> 6x - 12.11 = 0

=> 6( x - 2.11) = 0

=> 6 (x- 22) = 0

=> x-22=0

=> x = 22

vậy x = 22

Cảm ơn bạn nhiều nha!

x3 + 3x =12.11
x.(3+3) = 132
x.6 = 132
x = 22

sửa

(5/2*x-3)/15=3/10

5/2*x-3=3/10*15

5/2*x-3=9/2

5/2*x=9/2+3=9/2+6/2

5/2*x=15/2

x=15/2:5/2

x=3

Tính nhanh 2×(15-5)+3×10-5×10 

Ai nhanh mk tick ✔