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NB
2
1 tháng 10 2016
A = (99-98).(99+98)+(97+96).(97-96)+......+(3-2).(3+2)+1
tự tính nữa đi nha bạn
S
22 tháng 11 2015
\(\left(2x-3\right)^2-3\left(x-2\right)\left(1-x\right)=\left(2+3x\right)^2-4\left(2-3x\right)\)
\(\Rightarrow4x^2-12x+9-3\left(-x^2+3x-2\right)=4+12x+9x^2-\left(8-12x\right)\)
\(\Rightarrow4x^2-12x+9+3x^2-9x+6-4-12x-9x^2+8-12x=0\)
\(\Rightarrow-2x^2-45x+19=0\)
Có: \(\Delta=\left(-45\right)^2-4.\left(-2\right).19=2177\)
\(\Rightarrow\sqrt{\Delta}=\sqrt{2177}\)
\(\Rightarrow x=-\frac{45+\sqrt{2177}}{4}\) (nhận) hoặc \(x=-\frac{45-\sqrt{2177}}{4}\) (nhận)
HA
13 tháng 10 2015
Computers have become part of our daily lives.We visit shops,offices,and places of scenic beauty with the help of computers.We pay bills prepared by computers.We read newspapers and magazines which have been produced on computers.We receive letters from and send letters to almost every part of the world with the help of computers.And we can even learn foreign languages on computers.
What make a computer such a miraculous device?Each time you turn it on,with appropriate hardware and software,it is capable of doing almost anything you ask it to.It is calculating machine which speeds up calculation: it can add,subtract,multiply,and divide with lightning speed and perfect accuracy.
It is an electronic storage device which manages large collections of data.It is a magical typewriter which allows you to type and print any kind of document_letters,memos or requests for leave.It is a personal communicator which help you to interact with other computer and with people around the world.And if you **** entertainment,you can relax by playing computer games or listening to computer-played music.
NT
19
15 tháng 8 2017
Vì \(a>b>0\Rightarrow A=\frac{a+b}{a-b}>0\)
\(2a^2+2b^2=5ab\Rightarrow a^2+b^2=\frac{5ab}{2}\)
Ta có : \(E^2=\frac{\left(a+b\right)^2}{\left(a-b\right)^2}=\frac{a^2+b^2+2ab}{a^2+b^2-2ab}=\frac{\frac{5ab}{2}+2ab}{\frac{5ab}{2}-2ab}=\frac{\frac{9}{2}ab}{\frac{1}{2}ab}=\frac{\frac{9}{2}}{\frac{1}{2}}=9\)
\(E^2=9\Rightarrow E=3\)(vì E>0)
Vậy \(E=3\)
15 tháng 8 2017
Có : \(2a^2+2b^2=5ab\Rightarrow\hept{\begin{cases}2a^2+2b^2-4ab=ab\\2a^2+2b^2+4ab=9ab\end{cases}}\Rightarrow\hept{\begin{cases}2\left(a-b\right)^2=ab\\2\left(a+b\right)^2=9ab\end{cases}}\Rightarrow\hept{\begin{cases}a-b=\sqrt{\frac{ab}{2}}\\a+b=\sqrt{\frac{9ab}{2}}\end{cases}}\)
\(\Rightarrow E=\frac{\sqrt{\frac{9ab}{2}}}{\sqrt{\frac{ab}{2}}}=\sqrt{\frac{\frac{9ab}{2}}{\frac{ab}{2}}}=\sqrt{\frac{9ab}{2}.\frac{2}{ab}}=\sqrt{9}=3\)
TT
1
22 tháng 2 2016
tính trong ngoặc trước đi
mà bài này của lớp 9 ak?
duyệt đi
TT
0
2x5=10
10 dễ ợt