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Ta có:
D=2x2+3y2+4xy−8x−2y+18C=2x2+3y2+4xy−8x−2y+18
D=2(x2+2xy+y2)+y2−8x−2y+18C=2(x2+2xy+y2)+y2−8x−2y+18
D=2[(x+y)2−4(x+y)+4]+(y2+6y+9)+1C=2[(x+y)2−4(x+y)+4]+(y2+6y+9)+1
D=2(x+y−2)2+(y+3)2+1≥1C=2(x+y−2)2+(y+3)2+1≥1
Dấu "=" xảy ra ⇔x+y=2⇔x+y=2và y=−3y=−3
Hay x = 5 , y = -3
Đc chx bạn
\(a.10x\left(x-y\right)-6y\left(y-x\right)\\ =10x\left(x-y\right)+6y\left(x-y\right)\\ =\left(10x-6y\right)\left(x-y\right)\\ =2\left(5x-3y\right)\left(x-y\right)\)
\(b.14x^2y-21xy^2+28x^3y^2\\ =7xy\left(x-y+xy\right)\)
\(c.x^2-4+\left(x-2\right)^2\\ =\left(x-2\right)\left(x+2\right)+\left(x-2\right)^2\\ =\left(x-2\right)\left(x+2+x-2\right)\\ =2x\left(x-2\right)\)
\(d.\left(x+1\right)^2-25\\ =\left(x+1-5\right)\left(x+1+5\right)=\left(x-4\right)\left(x+6\right)\)
Bài 1:
a: ĐKXĐ: \(x+4\ne0\)
=>\(x\ne-4\)
b: ĐKXĐ: \(2x-1\ne0\)
=>\(2x\ne1\)
=>\(x\ne\dfrac{1}{2}\)
c: ĐKXĐ: \(x\left(y-3\right)\ne0\)
=>\(\left\{{}\begin{matrix}x\ne0\\y-3\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne0\\y\ne3\end{matrix}\right.\)
d: ĐKXĐ: \(x^2-4y^2\ne0\)
=>\(\left(x-2y\right)\left(x+2y\right)\ne0\)
=>\(x\ne\pm2y\)
e: ĐKXĐ: \(\left(5-x\right)\left(y+2\right)\ne0\)
=>\(\left\{{}\begin{matrix}x\ne5\\y\ne-2\end{matrix}\right.\)
Bài 2:
a: \(\dfrac{-12x^3y^2}{-20x^2y^2}=\dfrac{12x^3y^2}{20x^2y^2}=\dfrac{12x^3y^2:4x^2y^2}{20x^2y^2:4x^2y^2}=\dfrac{3x}{5}\)
b: \(\dfrac{x^2+xy-x-y}{x^2-xy-x+y}\)
\(=\dfrac{\left(x^2+xy\right)-\left(x+y\right)}{\left(x^2-xy\right)-\left(x-y\right)}\)
\(=\dfrac{x\left(x+y\right)-\left(x+y\right)}{x\left(x-y\right)-\left(x-y\right)}=\dfrac{\left(x+y\right)\left(x-1\right)}{\left(x-y\right)\left(x-1\right)}\)
\(=\dfrac{x+y}{x-y}\)
c: \(\dfrac{7x^2-7xy}{y^2-x^2}\)
\(=\dfrac{7x\left(x-y\right)}{\left(y-x\right)\left(y+x\right)}\)
\(=\dfrac{-7x\left(x-y\right)}{\left(x-y\right)\left(x+y\right)}=\dfrac{-7x}{x+y}\)
d: \(\dfrac{7x^2+14x+7}{3x^2+3x}\)
\(=\dfrac{7\left(x^2+2x+1\right)}{3x\left(x+1\right)}\)
\(=\dfrac{7\left(x+1\right)^2}{3x\left(x+1\right)}=\dfrac{7\left(x+1\right)}{3x}\)
e: \(\dfrac{3y-2-3xy+2x}{1-3x-x^3+3x^2}\)
\(=\dfrac{3y-2-x\left(3y-2\right)}{1-3x+3x^2-x^3}\)
\(=\dfrac{\left(3y-2\right)\left(1-x\right)}{\left(1-x\right)^3}=\dfrac{3y-2}{\left(1-x\right)^2}\)
g: \(\dfrac{x^2+7x+12}{x^2+5x+6}\)
\(=\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x+3\right)\left(x+2\right)}\)
\(=\dfrac{x+4}{x+2}\)
mk ghi đáp án, ko phân tích đc thì IB mk
a) \(x^2+6xy+9y^2=\left(x+3y\right)^2\)
b) \(4a^4-4a^2b^2+b^4=\left(2a^2-b^2\right)^2\)
c) \(x^6+y^2-2x^3y=\left(x^3-y\right)^2\)
d) \(\left(x+y\right)^3-\left(x-y\right)^3=2y\left(3x^2+y^2\right)\)
e) \(25x^4-10x^2y^2+y^4=\left(5x^2-y^2\right)^2\)
f) \(-a^2-2a-1=-\left(a+1\right)^2\)
g) \(27b^3-8a^3=\left(3b-2a\right)\left(9b^2+6ab+4a^2\right)\)
h) \(x^3+9x^2y+27xy^2+27y^3=\left(x+3y\right)^3\)
i) \(16x^2-9\left(x+y\right)^2=\left(x-3y\right)\left(7x+3y\right)\)
A=\(\left(x-y\right)^2+\left(x+y\right)^2=x^2-2xy+y^2+x^2+2xy+y^2=2x^2+2y^2\)
B=\(\left(x+y\right)^2-\left(x-y\right)^2=\left(x+y-x+y\right)\left(x+y+x-y\right)=\left(2y\right).\left(2x\right)\)
C=\(\left(2a+b\right)^2-\left(2a-b\right)^2=\left(2a+b-2a+b\right)\left(2a+b+2a-b\right)=\left(2b\right).\left(4a\right)\)
D=\(\left(2x-1\right)^2-2\left(2x-3\right)^2+4=4x^2-4x+1-4x+6+4=4x^2-8x+11\)
E=\(\left(x+3y\right)^2-\left(x-3y\right)^2=\left(x+3y-x+3y\right)\left(x+3y+x-3y\right)=\left(6y\right).\left(2x\right)\)
F=\(\left(2x+y\right)^2-\left(2x-y\right)^2=\left(2x+y-2x+y\right)\left(2x+y+2x-y\right)=\left(2y\right).\left(4x\right)\)
G=\(\left(x-2y\right)^2+4\left(x-2y\right)y+4y^2=x^2-4xy+4y^2+4xy-8y^2+4y^2=x^2\)
H=\(\left(x-y\right)^2-4\left(x-y\right)\left(x+2y\right)+4\left(x+2y^{ }\right)^2=x^2-2xy+y^2-4\left(x^2+2xy-xy-2y^2\right)+4x+8y=x^2-2xy+y^2-4x^2-8xy+4xy+8y^2+4x+8y=3x^2+12xy-9y^2+4x+8y\)
Ta có:
a) A= (x-y)^2 + (x+y)^2
A= x^2 -2xy + y^2 + x^2 + 2xy + y^2
A= 2x^2+ 2y^2
b) B= (x+y)^2 -( x-y)^2
B= (x+y-x+y)(x+y+x-y)
B= 2y.2x= 4xy
c) C= (2a+b)^2 -( 2a-b)^2
C= (2a+b-2a+b)(2a+b+2a-b)
C= 2b.4a
C= 8ab
d) D= (2x-1)^2 -2(2x-3)^2+4
D= 4x^2 -4x+1 -2( 4x^2 -12x + 9) +4
D= 4x^2 -4x+1 -8x^2 + 24x -18 +4
D= -4x^2 + 20x-13
e) E= (x+3y)^2-(x-3y)^2
E= (x+3y-x+3y)(x+3y+x-3y)
E= 6y.2x= 12xy
f) F= (2x+y)^2-(2x-y)^2
F=(2x+y-2x+y)(2x+y+2x-y)
F= 2y.4x= 8xy
g) G= (x-2y)^2 + 4(x-2y)y + 4y^2
G= (x-2y)^2 + 2(x-2y)2y + (2y)^2
G= (x-2y+2y)^2
G= x^2
h) H= (x-y)^2 -4(x-y)(x+2y)+ 4(x+2y)^2
H= (x-y)^2 - 2(x-y)2(x+2y) + [2(x+2y)]^2
H= (x-y- 2x-4y)^2
H= (-x-5y)^2
Lưu ý (-A-B)^2 = ( A+ B)^2
=> H= (x+5y)^2