Select the synonym of the following bold and underlined word in each sentence in the unit

To conserve electricity, we are cutting down on our central heating.

A. protec

B. hold

C. make

D. do

a) Xét \(\Delta ABK\left(\widehat{BAK}=90^0\right)\)

\(\Rightarrow BK^2=AB^2+AK^2\left(đ.lyPTG\right)\\ \Rightarrow BK^2=\left(AH^2+BH^2\right)+\left(AE^2+EK^2\right)\\ \Rightarrow BK^2=DE^2+\left(BH^2+DH^2\right)+\left(DK^2-DE^2\right)\left(AE=DH;AH=DE;EK^2=DK^2-DE^2\right)\\ \Rightarrow BK^2=BD^2+DK^2\left(BH^2+DH^2=BD^2\right)\\ \)

=> Tam giác BDK vuông tại D ( đ.lý PTG đảo )

=> góc BDK = 90 độ

sao cac bn biet la so do giai thich di

\(x-2\sqrt{x}=0\\ \Rightarrow\sqrt{x}\left(\sqrt{x}-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=0\\\sqrt{x}-2=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=4\end{matrix}\right.\)

b.

\(x=\sqrt{x}\\ \Leftrightarrow x-\sqrt{x}=0\\ \Leftrightarrow\sqrt{x}\left(\sqrt{x}-1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)

làm quyên bài luôn i

chiều dài nhân chiều rộng

S=1+2+2^2+2^3+...+2^2002

2S=2+2^2+2^3+2^4+...+2^2003

2S-S=(2+2^2+2^3+2^4+...+2^2003)-(1+2+2^2+2^3+...+2^2002)

2S-S=(2-2)+(2^2-2^2)+(2^3-2^3)+...+(2^2002-2^2002)+(2^2003-1)

S=0+0+0+...+0+(2^2003-1)

S=2^2003-1 (rút gọn)

tick nha

\(B=\left|x-3\right|+\left|4+x\right|\\ =\left|3-x\right|+\left|4+x\right|\\ \ge\left|3-x+4+x\right|\\ =7\)

Dấu "=" xảy ra khi

\(\left(3-x\right)\left(x+4\right)\ge0\\ \Leftrightarrow\left\{{}\begin{matrix}3-x\ge0\\x+4\ge0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}x\le3\\x\ge-4\end{matrix}\right.\\ \Leftrightarrow-4\le x\le3\)

Min A=7 khi \(-4\le x\le3\)

\(xy-5x+2y=30\\ \Rightarrow\left(xy-5x\right)+\left(2y-10\right)=20\\ \Rightarrow x\left(y-5\right)+2\left(y-5\right)=20\\ \Rightarrow\left(x+2\right)\left(y-5\right)=20\\ \Rightarrow x+2;y-5\in U\left(20\right)\)

Tìm x xng rồi tính !!