\(2x\left(x-5\right)-x\left(3+2x\right)=26\)

\(\Leftrightarrow2x^2-10x-3x-2x^2=26\)

\(\Leftrightarrow-13x=26\)

\(\Leftrightarrow x=-2\)

Bài làm:

Ta có: \(2x\left(x-5\right)-x\left(3+2x\right)=26\)

\(\Leftrightarrow2x^2-10x-3x-2x^2-26=0\)

\(\Leftrightarrow-13x=26\)

\(\Rightarrow x=-2\)

                                                      A B C O 1 1

Xét \(\Delta BOC\)có : \(\widehat{B}+\widehat{O}+\widehat{C}=180^o\)( ĐL tổng 3 góc trong 1 tam giác )

                          \(\widehat{B}+126^o+\widehat{C}=180^o\)

A B C O

Giải :

Xét tam giác BOC :

           \(\widehat{OBC}+\widehat{OCB}=180^o-126^o=54^o\)

Vì BO, CO là phân giác nên : \(\widehat{OBC}=\frac{1}{2}\widehat{ABC}\)và \(\widehat{OCB}=\frac{1}{2}\widehat{ACB}\)

\(\Rightarrow\widehat{ABC}+\widehat{ACB}=2.54=108^o\)

Xét tam giác ABC :

\(\Rightarrow\widehat{BAC}=180-108=72^o\)

 Mình cho bạn công thức tổng quát luôn nè : \(\widehat{BOC}=\frac{180^o-\widehat{BAC}}{2}\)

She is not only a teacher, she is also a singer
=> Not only is she a teacher but she also is a singer

She is not only a teacher, she is also a singer. 

=> Not only is she a teacher, she is also a singer.

Ta có : \(B=x.\left(x^2+x+1\right)-x^2.\left(x+1\right)-x+5\)

\(=x^3-x^2-x-x^3-x^2-x+5\)

\(=5\) không phụ thuộc vào giá trị biến \(x\)

B = x( x² + x + 1 ) - x²( x + 1 ) - x + 5

B = x³ + x² + x - x³ - x² - x + 5

B = 5 

=> đpcm

Tự tìm trên mạng đi bạn nhớ

Một đống mà gõ cho bạn đến bao giờ 

công thức môn gì dậy bạn

a.x = -3

b.\(\frac{13}{2}\)

c. (x+4)²

d. không bik

Bài làm:

a) \(\left(x+4\right)^2-1=0\)

\(\Leftrightarrow\left(x+4\right)^2=1\)

\(\Leftrightarrow\orbr{\begin{cases}x+4=1\\x+4=-1\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=-5\end{cases}}\)

b) \(\left(2x-3\right)^2=100\)

\(\Leftrightarrow\orbr{\begin{cases}2x-3=10\\2x-3=-10\end{cases}}\Leftrightarrow\orbr{\begin{cases}2x=13\\2x=-7\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{13}{2}\\x=-\frac{7}{2}\end{cases}}\)

c) \(x^2+8x+16=0\)

\(\Leftrightarrow\left(x+4\right)^2=0\)

\(\Rightarrow x+4=0\)

\(\Rightarrow x=-4\)

d) \(4x^2-12x=-9\)

\(\Leftrightarrow4x^2-12x+9=0\)

\(\Leftrightarrow\left(2x-3\right)^2=0\)

\(\Rightarrow2x-3=0\)

\(\Rightarrow x=\frac{3}{2}\)

a) \(\frac{\sqrt{7-4\sqrt{3}}}{\sqrt{2-\sqrt{3}}}\cdot\sqrt{2+\sqrt{3}}\)

\(=\frac{\sqrt{4-2.2.\sqrt{3}+3}}{\sqrt{2-\sqrt{3}}}\cdot\frac{\sqrt{4+2\sqrt{3}}}{\sqrt{2}}\)

\(=\frac{\sqrt{\left(2-\sqrt{3}\right)^2}}{\sqrt{4-2\sqrt{3}}}\cdot\sqrt{\left(1+\sqrt{3}\right)^2}\)

\(=\frac{2-\sqrt{3}}{\sqrt{3}-1}\cdot\left(1+\sqrt{3}\right)\)

\(=\frac{\left(2-\sqrt{3}\right)\left(1+\sqrt{3}\right)^2}{2}\) 

b) \(\sqrt{\frac{3}{20}}+\sqrt{\frac{1}{60}}-2\sqrt{\frac{1}{50}}\)

\(=\sqrt{\frac{1}{10}\cdot\frac{3}{2}}+\sqrt{\frac{1}{10}\cdot\frac{1}{6}}-2\sqrt{\frac{1}{10}\cdot\frac{1}{5}}\)

\(=\sqrt{\frac{1}{10}}\cdot\left(\sqrt{\frac{3}{2}}+\sqrt{\frac{1}{6}}-2\sqrt{\frac{1}{5}}\right)\)

\(=\frac{1}{\sqrt{10}}\cdot\left(\frac{\sqrt{6}}{2}+\frac{\sqrt{6}}{6}-\frac{2\sqrt{5}}{5}\right)\)

\(=\frac{1}{\sqrt{10}}\cdot\left(\frac{15\sqrt{6}+5\sqrt{6}-12\sqrt{5}}{6}\right)\)

\(=\frac{2.\left(5\sqrt{6}-3\sqrt{5}\right)}{3\sqrt{10}}\cdot\)

......

1, electricity gas and water are ..........necessities..........in western countries  NEED

2, there has been some........reduction.........in unemployment  REDUCE

3, there are lots oof technological.........innovations..........designed to save energy INNOVATE

4, I switched the light off to save.........electricity..........ELECTRIC

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