A = x² - 20x + 100 = x² - 2.x.10 + 10² = ( x - 10 )² = ( 20 - 10 )² = 10² = 100

B = ( x + 2 )² + 2( x + 2 )( 3x + 5 ) + ( 3x + 5 )² ( vầy thôi nhỉ ? )

= [ ( x + 2 ) + ( 3x + 5 ) ]²

= ( x + 2 + 3x + 5 )²

= ( 4x + 7 )²

= \(\left[4\cdot\left(-\frac{1}{4}\right)+7\right]^2\)

= ( -1 + 7 )² = 6² = 36

gíup mình nha 

a, \(\frac{2x}{5}+\frac{3-2x}{3}\ge\frac{3x+2}{2}\)

\(\Leftrightarrow\frac{12x}{30}+\frac{30-20x}{30}\ge\frac{45x+30}{30}\)

\(\Leftrightarrow12x+30-20x\ge45x+30\)

\(\Leftrightarrow-8x+30\ge45x+30\Leftrightarrow-8x-45x\ge0\)

\(\Leftrightarrow-53x\ge0\Leftrightarrow x\le0\)

Vậy tập nghiệm của BFT là S = { x | x =< 0 } 

\(a,2x\left(x-5\right)+4\left(x-5\right)=0\\ \Leftrightarrow\left(x-5\right)\left(2x+4\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-5=0\\2x+4=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\2x=-4\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-2\end{matrix}\right.\)

Vậy \(x\in\left\{5;-2\right\}\)

\(b,3x-15=2x\left(x-5\right)\\ \Leftrightarrow3\left(x-5\right)-2x\left(x-5\right)=0\\ \Leftrightarrow\left(x-5\right)\left(-2x+3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-5=0\\-2x+3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\2x=3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=\dfrac{3}{2}\end{matrix}\right.\)

Vậy \(x\in\left\{5;\dfrac{3}{2}\right\}\)

\(c,\left(2x+1\right)\left(3x-2\right)=\left(5x-8\right)\left(2x+1\right)\\ \Leftrightarrow\left(2x+1\right)\left(3x-2\right)-\left(5x-8\right)\left(2x+1\right)=0\\ \Leftrightarrow\left(2x+1\right)\left(3x-2-5x+8\right)=0\\ \Leftrightarrow\left(2x+1\right)\left(-2x+6\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}2x+1=0\\-2x+6=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}2x=-1\\2x=6\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=3\end{matrix}\right.\)

Vậy \(x\in\left\{-\dfrac{1}{2};3\right\}\)

Câu d xem lại đề

có ai giúp mình câu c và d không mình đang cần gấp

Bài 2: 

a: \(A=\left(x+1\right)^3+5=20^3+5=8005\)

b: \(B=\left(x-1\right)^3+1=10^3+1=1001\)

Chọn B.

Ta có:

Vậy