https://hoidap247.com/cau-hoi/4602014

nì nì :> 

kh hề a :") 

:> một màn diễn cực gắt 

\(a,\\ M+\left(2x^3+3x^2y-3xy^2+xy+1\right)=3x^3+3x^3y-3xy^2+xy\\ M=\left(3x^3+3x^3y-3xy^2+xy\right)-\left(2x^3+2x^2y-2xy^2+xy+1\right)\\ M=3x^3+3x^3y-3xy^2+xy-2x^3-2x^2y+2xy^2-xy-1\\ M=\left(3x^3-2x^3\right)+\left(3x^2y-2x^2y\right)+\left(3xy^2-2xy^2\right)+\left(xy-xy\right)\\ M=x^3+1\)

:0 cam hơi mờ cj oi 

Hình :

Xét `Delta ACH` và `Dela BCK` có :

`hat(C)` chung 

\(\widehat{AHC}=\widehat{BKC}=90^0\\ \Rightarrow\Delta CAN\sim\Delta CBK\\ \Rightarrow\dfrac{CH}{CK}=\dfrac{AH}{BK}\\ \Rightarrow CH\cdot BK=CK\cdot AH\\ \Rightarrow CH^2\cdot BK^2=CK^2\cdot AH^2\\ \Rightarrow AH^2\cdot CK^2=\dfrac{BK^2\cdot BC^2}{4}\\ \Rightarrow AH^2\left(BC^2-BK^2\right)=\dfrac{BK^2\cdot BC^2}{4}\)

chia cả hai vế cho \(AH^2\cdot BC^2\cdot BK^2\)

\(\Rightarrow\dfrac{1}{BK^2}-\dfrac{1}{BC^2}=\dfrac{1}{4AH^2}\\ \Rightarrow\dfrac{1}{BC^2}+\dfrac{1}{4AH^2}=\dfrac{1}{BK^2}\left(\text{đ}pcm\right)\)

\(\sqrt{x-3}=2\)

`<=>x-3=4`

`<=>x=7`