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\(x^2-4x-1=0\)
\(\left(x^2-2\cdot x\cdot2+4\right)-5=0\)
\(\left(x-2\right)^2=\left(\sqrt{5}\right)^2\)
\(\Rightarrow x-2=\pm\sqrt{5}\)
Tự giải tiếp nha ...
A= 2006 X 2008 - 20072
A = 2006 . 2008 - 2007 . 2007
A = 2006 . ( 2007 + 1 ) - 2007 . ( 2006 + 1 )
A = 2006 . 2007 + 2006 - 2007 . 2006 + 2007
A = -1
B= 2016 X 2018 - 20172
B= 2016 . 2018 - 2017 . 2017
B = 2016 . ( 2017 + 1 ) - 2017 . ( 2016 + 1 )
B = 2016 . 2017 + 2016 - 2017 . 2016 + 2017
B = -1
ab2+ac2+abc+a2b+bc2+abc+a2c+b2c+abc
=ab2+ac2+a2b+bc2+a2c+b2c+3abc
\(4x^2-4\)
\(=4\left(x^2-1\right)\)
\(=4\left(x-1\right)\left(x+1\right)\)
4a) \(\left(a+b\right)^2=a^2+2ab+b^2\)
\(\left(a-b\right)^2+4ab=a^2-2ab+b^2+4ab=a^2+b^2+2ab\)
=> (a+b)^2=(a-b)^2+4ab
- 2x – x2 + 2 – x – (3x2 + 6x + 5x +10) = – 4x2 + 2
- 2x – x2 + 2 – x – 3x2 – 6x – 5x – 10 = – 4x2 + 2 –10x = 10 x = – 1
- 2x2 – 6x + x – 3 = 0
(x – 3)(2x + 1) = 0
x = 3 hay x = -1/2
\(136^2+16^2-20^2-32\cdot136\\ =\left(136^2-32\cdot136+16^2\right)-20^2\\ =\left(136-16\right)^2-20^2=120^2-20^2\\ =\left(120-20\right)\left(120+20\right)\\ =100\cdot140=14000\)
Tick plz
Ta có: \(B=136^2-32\cdot136+16^2-20^2\)
\(=120^2-20^2\)
\(=100\cdot140=14000\)