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1. 208 - 24 x y = bao nhiêu ???

   19:57
2.      

Ta có: \(\frac{36}{x+6}+\frac{36}{x-6}=\frac{9}{2}\)

ĐKXĐ: \(\left\{\begin{matrix}x\ne-6\\x\ne6\end{matrix}\right.\)

\(\Leftrightarrow36\left(\frac{1}{x+6}+\frac{1}{x-6}\right)=\frac{9}{2}\)

\(\Leftrightarrow36\left(\frac{x-6+x+6}{\left(x+6\right)\left(x-6\right)}\right)=\frac{9}{2}\)

\(\Leftrightarrow36.\frac{2x}{x^2-36}=\frac{9}{2}\)

\(\Leftrightarrow\frac{72x}{x^2-36}=\frac{9}{2}\)

\(\Leftrightarrow72x.2=9.\left(x^2-36\right)\)

\(\Leftrightarrow8x.2=x^2-36\) ( chia cả hai vế cho 9 )

\(\Leftrightarrow16x=x^2-36\)

\(\Leftrightarrow16x-x^2+36=0\)

\(\Leftrightarrow-x^2+16x+36=0\)

\(\Leftrightarrow x^2-16x-36=0\)

\(\Leftrightarrow x^2+2x-18x-36=0\)

\(\Leftrightarrow x\left(x+2\right)-18\left(x+2\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(x-18\right)=0\)

\(\Leftrightarrow\left[\begin{matrix}x+2=0\\x-18=0\end{matrix}\right.\Leftrightarrow\left[\begin{matrix}x=-2\\x=18\end{matrix}\right.\)

Vậy: \(x=-2;18\)

\(\frac{36}{x+6}+\frac{36}{x-6}=4,5\left(đkxđ:x\ne\pm6\right)\)

\(\Leftrightarrow\frac{36\left(x-6\right)+36\left(x+6\right)}{\left(x-6\right)\left(x+6\right)}=\frac{4,5\left(x-6\right)\left(x+6\right)}{\left(x-6\right)\left(x+6\right)}\)

\(\Leftrightarrow\frac{36\left(x-6+x+6\right)}{\left(x-6\right)\left(x+6\right)}=\frac{4,5\left(x^2-36\right)}{\left(x-6\right)\left(x+6\right)}\)

\(\Rightarrow36\times2x=4,5\left(x^2-36\right)\)

\(\Leftrightarrow72x=4,5x^2-162\)

\(\Leftrightarrow4,5x^2-72x-162=0\)

\(\Leftrightarrow4,5x^2+9x-81x-162=0\)

\(\Leftrightarrow4,5x\left(x+2\right)-81\left(x+2\right)=0\)

\(\Leftrightarrow\left(4,5x-81\right)\left(x+2\right)=0\)

\(\Leftrightarrow\left[\begin{matrix}4,5x-81=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[\begin{matrix}x=18\\x=-2\end{matrix}\right.\left(TMĐKXĐ\right)\)

a: \(\frac{52}{17}>\frac{51}{17}=3\)

\(3=\frac{121}{41}>\frac{120}{41}\)

Do đó: \(\frac{52}{17}>\frac{120}{41}\)

b: \(\frac34+\frac14:\left(\frac{7}{12}-\frac16\right)\)

\(=\frac34+\frac14:\left(\frac{7}{12}-\frac{2}{12}\right)\)

\(=\frac34+\frac14:\frac{5}{12}\)

\(=\frac34+\frac14\times\frac{12}{5}=\frac34+\frac35=\frac{15}{20}+\frac{12}{20}=\frac{27}{20}\)

c: \(372,463\cdot998+744,926\)

\(=372,463\cdot998+372,463\cdot2\)

\(=372,463\times\left(998+2\right)=372,463\times1000=372463\)

d: Số số hạng trong dãy số 2;4;6;...;100 là:

\(\left(100-2\right):2+1=98:2+1=49+1=50\) (số)

\(2-4+6-8+10-12+\cdots+98-100+102\)

\(=\left(2-4\right)+\left(6-8\right)+\cdots+\left(98-100\right)+102\)

=(-2)+(-2)+...+(-2)+102

\(=-2\cdot\frac{50}{2}+102=-50+102=52\)

e: (y+112)-113=79

=>y+112-113=79

=>y-1=79

=>y=79+1=80

f: \(\frac34-y=\frac12\)

=>\(y=\frac34-\frac12=\frac14\)

g: \(\left(\frac45-2\times y\right)+\frac16=\frac56\)

=>\(\frac45-2\times y=\frac56-\frac16=\frac46=\frac23\)

=>\(2\times y=\frac45-\frac23=\frac{12}{15}-\frac{10}{15}=\frac{2}{15}\)

=>\(y=\frac{2}{15}:2=\frac{1}{15}\)

h: (y+1)+(y+2)+...+(y+50)=1750

=>50y+(1+2+...+50)=1750

=>\(50y+50\times\frac{51}{2}=1750\)

=>50y+1275=1750

=>50y=1750-1275=475

=>\(y=\frac{475}{50}=9,5\)

Đáp án: 

3c

4d

5a

6c

7b

8b

9a

10d

Vote cho mik vs nha.

5)13/15

6)24

7)25

8)4537

\(-23.63+23.21-58.23\\ =23.\left(-63\right)+23.21-58.23\\ =23\left(-63+21-58\right)\\ =23.\left(-100\right)=-2300\)

-23 . 63 + 23 . 21 - 58 . 23

= 23 . (-63 + 21 - 58) = 23 . (-100) = -2300