\(\left(38-x\right)\left(x+25\right)=0\\ \Rightarrow\left[{}\begin{matrix}38-x=0\\x+25=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=38\\x=-25\end{matrix}\right.\)

(38 – x). (x + 25) = 0

Suy ra 38 – x = 0 hoặc x + 25 = 0

Trường hợp 1:

38 – x = 0

x = 38 – 0

x = 38

Trường hợp 2:

x + 25 = 0

x = 0 – 25

x = -25

Vậy x = 38, x = -25.

\(x\in\left\{38;-25\right\}\)

\(\left(38-x\right)\left(25+x\right)=0\)

\(\Rightarrow38-x=0\) hoặc \(25+x=0\)

*) \(38-x=0\)

\(x=38\)

*) \(25+x=0\)

\(x=0-25\)

\(x=-25\)

Vậy \(x=-25;x=38\)

\(=>\left[{}\begin{matrix}38-x=0\\x+25=0\end{matrix}\right.=>\left[{}\begin{matrix}x=38\\x=-25\end{matrix}\right.\)
Vậy \(x\in\left\{38;-25\right\}\)

\(=\left(\dfrac{32}{99}-\dfrac{14}{9}-\dfrac{25}{99}\right)\cdot\dfrac{11}{38}\)

\(=\left(\dfrac{7}{99}-\dfrac{154}{99}\right)\cdot\dfrac{11}{38}\)

\(=\dfrac{-147}{99}\cdot\dfrac{11}{38}=\dfrac{-49}{114}\)

\(\left(x^2-25\right)\left(x^2+1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x^2-25=0\\x^2+1=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x^2=25\\x^2=1\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}\orbr{\begin{cases}x=5\\x=-5\end{cases}}\\\orbr{\begin{cases}x=1\\x=-1\end{cases}}\end{cases}}\)

\(3\left(x^2-4\right)-\left(2x^2-1\right)=38\)

\(3x^2-12-2x^2+1=38\)

\(\left(3x^2-2x^2\right)-12+1=38\)

\(1x^2-11=38\)

\(x^2=49\)

\(\Rightarrow\orbr{\begin{cases}x=7\\x=-7\end{cases}}\)

Thiếu :(

\(x^2=25\Rightarrow\orbr{\begin{cases}x=5\\x=-5\end{cases}}\)

\(x^2=1\Rightarrow\orbr{\begin{cases}x=1\\x=-1\end{cases}}\)

(x²-25)(x²+1)=0

=> x²-25=0 (vì x²+1 >0 với mọi x)

<=> \(\orbr{\begin{cases}x=5\\x=-5\end{cases}}\)

b) 3(x²-4)-(2x²-1)=38

<=> 3x²-12-2x²+1-38=0

<=> x²-49=0

<=> x²=49

\(\Leftrightarrow\orbr{\begin{cases}x=7\\x=-7\end{cases}}\)

35 . 34 + 35 . 38 + 65 . 75 + 65 . 45 + 35 . 34 = 

= 35 . 34 + 35 . 38 + 35 . 34 + 65 . 75 + 65 . 45 

= 35 . ( 34 + 38 + 34 ) + 65 . ( 75 + 45 )

=  35 . 110  + 65 . 110 

= 110 . ( 35 + 65 ) 

= 110 . 100

= 11000

Hok tốt!!!!!!!!!!!!!

a) Tính bằng cách hợp lí nhất :

35 . 34 + 35 . 38 + 65 . 75 + 65 . 45 + 35 . 34

= 35 . 34 + 35 . 38 + 35 . 34 + 65 . 75 + 65 . 45

= 35 . ( 34 + 38 + 34 ) + 65 . ( 75 + 45 )

= 35 . 106 + 65 . 120

= 3710 + 7800

= 11510

3 . 25 . 8 + 4 . 37 . 6 + 2 . 38 . 12

= 3 . 8 . 25 + 4 . 6 . 37 + 2 . 12 . 38

= 24 . 25 + 24 . 37 + 24 . 38

= 24 . ( 25 + 37 + 38 )

= 24 . 100

= 2400

b) Tìm số tự nhiên x, biết :

( x - 5 ) ( x + 7 ) = 0

\(\Rightarrow\orbr{\begin{cases}x-5=0\\x+7=0\end{cases}\Rightarrow\orbr{\begin{cases}x=5\\x=-7\end{cases}}}.\)

Vậy .......

3 . 25 . 8 + 4 . 37 . 6 + 2 . 38 . 12 = 

= 3 . 8 . 25 +  4 . 6 . 37 + 2 . 12 . 38

= 24 . 25 + 24 . 37 + 24 . 38

= 24 . ( 25 + 37 + 38 )

= 24 . 100 

= 2400

Hok tốt!!!!!!!!!!!