giúp mình với gấp lắm r=((
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1:
Khi x=36 thì \(A=\dfrac{6+4}{6-4}=\dfrac{10}{2}=5\)
2: \(B=\dfrac{3\sqrt{x}-12+16-2\sqrt{x}}{x-16}=\dfrac{\sqrt{x}+4}{x-16}=\dfrac{1}{\sqrt{x}-4}\)
3: A=B*|x-2|
=>|x-2|=A/B=căn x+4
=>x-2=căn x+4 hoặc x-2=-căn x-4
=>x-căn x-6=0 hoặc x+căn x+2=0
=>x=9
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 4:
a. \(\left\{{}\begin{matrix}R1=\dfrac{U1^2}{P1}=\dfrac{120^2}{40}=360\Omega\\R2=\dfrac{U2^2}{P2}=\dfrac{120^2}{60}=240\Omega\end{matrix}\right.\)
b. \(P1< P2=>\) đèn 2 sáng hơn.
c. \(U1+U2=120+120=240V=U=240V=>\) đèn sáng bình thường.
![](https://rs.olm.vn/images/avt/0.png?1311)
=>x+1/2+x+1/6+...+x+1/90=99,9
=>\(\left(x+x+...+x\right)+\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{90}\right)=99.9\)
=>\(9x+\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)=99.9\)
=>9x+(1-0,1)=99,9
=>9x=99,9+0,1-1=100-1=99
=>x=11
![](https://rs.olm.vn/images/avt/0.png?1311)
Em tham khảo:
Cách ngắt nhịp của hai dòng thơ:
Lặng rồi/ cả tiếng con ve,
Con ve cũng mệt/ vì hè nắng oi.
![](https://rs.olm.vn/images/avt/0.png?1311)
2(1-2x)-5=3(x+2)
=>\(2-4x-5=3x+6\)
=>\(-4x-3=3x+6\)
=>\(-7x=9\)
=>\(x=-\dfrac{9}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
II
1 B
2 C
3 A
4 D
5 C
6 B
III
1 Where do they live?
2 Why do you like "Tom and Jerry"
3 When do they do their homework?
4 What is that?
5 What vegetable do you like?
Bài 9:
Ta có: \(a-4+\sqrt{16-8a+a^2}\)
\(=a-4+\sqrt{\left(a-4\right)^2}\)
\(=a-4+a-4\)
=2a-8
a)\(\dfrac{x^2-3}{x^2+2x\sqrt{3}+3}=\dfrac{\left(x-\sqrt{3}\right)\left(x+\sqrt{3}\right)}{\left(x+\sqrt{3}\right)^2}=\dfrac{x-\sqrt{3}}{x+\sqrt{3}}\)
\(\dfrac{x^2-2x\sqrt{15}+15}{x^2-15}=\dfrac{\left(x-\sqrt{15}\right)^2}{\left(x-\sqrt{15}\right)\left(x+\sqrt{15}\right)}=\dfrac{x-\sqrt{15}}{x+\sqrt{15}}\)
\(\dfrac{4x^2-6}{4x^2-4x\sqrt{6}+6}=\dfrac{\left(2x-\sqrt{6}\right)\left(2x+\sqrt{6}\right)}{\left(2x-\sqrt{6}\right)^2}=\dfrac{2x+\sqrt{6}}{2x-\sqrt{6}}\)
b) \(\dfrac{a^2+2a\sqrt{8}+8}{a^2-8}=\dfrac{\left(a+\sqrt{8}\right)^2}{\left(a+\sqrt{8}\right)\left(a-\sqrt{8}\right)}=\dfrac{a+\sqrt{8}}{a-\sqrt{8}}\)
\(\dfrac{9x^2-15}{9x^2-6x\sqrt{15}+15}=\dfrac{\left(3x-\sqrt{15}\right)\left(3x+\sqrt{15}\right)}{\left(3x-\sqrt{15}\right)^2}=\dfrac{3x+\sqrt{15}}{3x-\sqrt{15}}\)
\(\dfrac{a^2-2a\sqrt{7}+7}{a^2-7}=\dfrac{\left(a-\sqrt{7}\right)^2}{\left(a-\sqrt{7}\right)\left(a+\sqrt{7}\right)}=\dfrac{a-\sqrt{7}}{a+\sqrt{7}}\)