C

C

55470 : 86 = 645

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a) \(\left(3-x\right)\left(5x+10\right)=0\)

\(\left(3-x\right).5.\left(x+2\right)=0\)

\(\Rightarrow\orbr{\begin{cases}3-x=0\\x+2=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=3\\x=-2\end{cases}}\)

vậy...

b) \(\left|5x+2\right|-4x=7\)

\(\left|5x+2\right|=7+4x\)

\(\Rightarrow\orbr{\begin{cases}5x+2=7+4x\\5x+2=-7-4x\end{cases}}\Rightarrow\orbr{\begin{cases}5x-4x=7-2\\5x+4x=-7-2\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=5\\9x=-9\end{cases}}\Rightarrow\orbr{\begin{cases}x=5\\x=-1\end{cases}}\)

vậy.... 

k nha 

a, \(\left(3-x\right)\left(5x+10\right)=0\)

\(\Rightarrow3-x=0\)   hoặc     \(5x+10=0\)

\(\Rightarrow x=3\)         hoặc          \(x=-2\)

3^2+4^2=5^2

9+16=25

MIK CẦN CÁCH LM MAK

324:6= 54 

sao lại =57 ?

\(x\times7=324+x\)

\(x\times7-x=324\)

\(x\times\left(7-1\right)=324\)

\(x\times6=324\)

\(x=324:6\)

\(x=57\)

a) \(P=\dfrac{A}{B}=\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{1}{x-\sqrt{x}}\right):\dfrac{\sqrt{x}+1}{x-1}\left(đk:x>0,x\ne1\right)\)

\(=\dfrac{x-1}{\sqrt{x}\left(\sqrt{x}-1\right)}.\dfrac{x-1}{\sqrt{x}+1}=\dfrac{\left(x-1\right)^2}{\sqrt{x}\left(x-1\right)}=\dfrac{x-1}{\sqrt{x}}\)

b) \(P\sqrt{x}=m+\sqrt{x}\)

\(\Leftrightarrow\dfrac{x-1}{\sqrt{x}}.\sqrt{x}=m+\sqrt[]{x}\)

\(\Leftrightarrow x-1=m+\sqrt{x}\)

\(\Leftrightarrow m=x-\sqrt{x}-1\)

Trả lời:

Ta có : 1.2²= 1.2.2=1.2.(3-1)=1.2.3-1.2

             2.3²= 2.3.3=2.3.(4-1)=2.3.4-2.3

.................................................

             98.99²= 98.99.99=98.99.(100-1)=98.99.100-98.99

A=1.2.3 - 1.2 + 2.3.4 - 2.3 + ... + 98.99.100 - 98.99 hay A=1.2.3 + 2.3.4 +...+ 98.99.100 - (1.2 + 2.3 + ... + 98.99) = B - C

B=1.2.3 + 2.3.4 + ... + 98.99.100

B.4=1.2.3.4 + 2.3.4.(5 - 1) + ... + 98.99.100.(101 - 97)= 98.99.100.101

=> 98.99.100.101:4= 24497550

C=1.2 + 2.3 + ... + 98.99 

C.3=1.2.3 + 2.3.(4 - 1) + ... + 98.99.(100 - 97)= 98.99.100

=> 98.99.100:3= 323400

Vậy A= 24497550 - 323400 = 24174150

@qqqqqqq cảm ơn bạn nhé! (^_^)

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