lớp 7 chắc làm tắt thế này cũng hiểu

a)2|x| +5=23

<=>2|x|=18

=>|x|=±9

b)ta xét th (x+5)(x+2)=0

=>Th1:x+5=0                            Th2:x+2=0

=>x=-5                                     =>x=-2

vì (x+5)(x+2)<0

=>\(x\in\left\{-\infty;-2;-5\right\}\)

c)(x+1)+(x+2)+(x+3)+..........+(x+100)=5750

<=>(x+x+..x)+(1+2+3+...+100)=5750

=>5050+100x=5750

=>100x=5750-5050

=>100x=700

=>x=7

Theo định lý Bezout, ta có:

f(x) chia x - 1 dư 5

--> f(1) = 5 --> 4 + a + b = 5

<=> a + b = 1 <=> b = 1 - a

f(x) chia x - 2 dư 23

--> f(2) = 23 --> 20 + 2a + b = 23

--> 2a + b = 3

<=> 2a + 1 - a = 3 <=> a = 2

--> b = -1

\(a,2x^2+y^2+6x-2xy+9=0\\ \Leftrightarrow\left(x^2-2xy+y^2\right)+\left(x^2+6x+9\right)=0\\ \Leftrightarrow\left(x-y\right)^2+\left(x+3\right)^2=0\\ \Leftrightarrow\left\{{}\begin{matrix}x=y\\x=-3\end{matrix}\right.\Leftrightarrow x=y=-3\\ b,A=\left(x-2021\right)^2+\left(x+2022\right)^2=x^2-4042x+2021^2+x^2+4044x+2022^2\\ A=2x^2+2x+2021^2+2022^2\\ A=2\left(x^2+x+\dfrac{1}{4}\right)+2021^2+2022^2-\dfrac{1}{2}\\ A=2\left(x+\dfrac{1}{2}\right)^2+2021^2+2022^2-\dfrac{1}{2}\ge2021^2+2022^2-\dfrac{1}{2}\\ A_{max}=2021^2+2022^2-\dfrac{1}{2}\Leftrightarrow x=-\dfrac{1}{2}\)\(c,P=\left(a+1\right)\left(a+3\right)\left(a+5\right)\left(a+7\right)+16\\ P=\left(a^2+8a+7\right)\left(a^2+8a+15\right)+16\\ P=\left(a^2+8a+11\right)^2-16+16=\left(a^2+8a+11\right)^2\left(Đpcm\right)\)

ko có biết

a, X=13,12

b,X=6

a) 10 + x = 23 .12

10 + x = 276

x = 276 -10

x=266

b) 23 - x= 34 :2

23-x=17

x = 23-17

x = 6

\(\frac{x-23}{24}+\frac{x-23}{25}=\frac{x-23}{26}+\frac{x-23}{27}\)

\(\frac{x-23}{24}+\frac{x-23}{25}-\frac{x-23}{26}-\frac{x-23}{27}=0\)

\(\left(x-23\right)\left(\frac{1}{24}+\frac{1}{25}-\frac{1}{26}-\frac{1}{27}\right)=0\)

=> x-23=0

x=0+23

x=23. Vậy x=23

Chúc bạn học tốt!^_^

\(\frac{x-23}{24}+\frac{x-23}{25}=\frac{x-23}{26}+\frac{x-23}{27}\) 

=> \(\frac{x-23}{24}+\frac{x-23}{25}-\frac{x-23}{26}-\frac{x-23}{27}=0\)

=>( x-13)(\(\frac{1}{24}+\frac{1}{25}-\frac{1}{26}-\frac{1}{27}\) = 0

ta thấy 1/24>1/25>1/26>1/27 => 1/24+1/25 - 1/ 26 - 1/17 > 0

=> x -13 = -

=> x=13