36a2 - 60ab + 25b2
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\(a,=\left(x+1\right)^2\\ b,=\left(y-2\right)^2\\ c,=\left(x-3\right)^2\\ d,=\left(a-7\right)^2\\ e,=\left(m-2\right)^2\\ f,=\left(2x-1\right)^2\\ g,=\left(a+5\right)^2\\ h,=\left(z-10^2\right)\\ i,=\left(x+3y\right)^2\\ j,=\left(2x-5b\right)^2\\ k,=\left(a+5\right)^2\\ l,=\left(x^2+1\right)^2\\ m,=\left(y^3-1\right)^2=\left(y-1\right)^2\left(y^2+y+1\right)^2\\ n,=\left(c^5-5\right)^2\\ o,=\left(3x^2+2y\right)^2\\ p,=5m^2n^3\left(5m^2n^3-2\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có
( a 2 + 9 ) 2 – 36 a 2 = ( a 2 + 9 ) 2 – ( 6 a ) 2 = ( a 2 + 9 + 6 a ) ( a 2 + 9 – 6 a ) = ( a + 3 ) 2 ( a – 3 ) 2
Đáp án cần chọn là: A
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\(a,Sửa:25x^2-20xy+4y^2=\left(5x-2y\right)^2\\ b,=\dfrac{1}{4}\left(\dfrac{1}{9}a^2-b^2\right)=\dfrac{1}{4}\left(\dfrac{1}{3}a-b\right)\left(\dfrac{1}{3}a+b\right)\\ c,=\dfrac{1}{8}\left(a+2\right)^3-1=\left[\dfrac{1}{2}\left(a+2\right)\right]^3-1=\left[\dfrac{1}{2}a+1\right]^3-1\\ =\left(\dfrac{1}{2}a+1-1\right)\left(\dfrac{1}{4}a^2+a+1+\dfrac{1}{2}a+1+1\right)\\ =\dfrac{1}{2}a\left(\dfrac{1}{4}a^2+\dfrac{3}{2}a+3\right)\\ d,=\left(x^3-1\right)\left(x^3+1\right)\\ =\left(x-1\right)\left(x+1\right)\left(x^2-x+1\right)\left(x^2+x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đơn thức - 36 a 2 . b 2 . x 2 . y 3 với a, b là hằng số có hệ số là - 36 a 2 . b 2
Chọn đáp án B
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(50x^5-8x^3\)
\(=2x^3\left(25x^2-4\right)\)
\(=2x^3\left(5x-2\right)\left(5x+2\right)\)
b: \(x^4-5x^2-4y^2+10y\)
\(=\left(x^2-2y\right)\left(x^2+2y\right)-5\left(x^2-2y\right)\)
\(=\left(x^2-2y\right)\left(x^2+2y-5\right)\)
c: \(36a^2+12a+1-b^2\)
\(=\left(6a+1\right)^2-b^2\)
\(=\left(6a+1-b\right)\left(6a+1+b\right)\)
d: \(x^3+y^3-xy^2-x^2y\)
\(=\left(x+y\right)\left(x^2-xy+y^2\right)-xy\left(x+y\right)\)
\(=\left(x+y\right)\left(x^2-2xy+y^2\right)\)
\(=\left(x+y\right)\cdot\left(x-y\right)^2\)
e: Ta có: \(4x^2+4x-3\)
\(=4x^2+6x-2x-3\)
\(=2x\left(2x+3\right)-\left(2x+3\right)\)
\(=\left(2x+3\right)\left(2x-1\right)\)
f: Ta có: \(9x^4+16x^2-4\)
\(=9x^4+18x^2-2x^2-4\)
\(=9x^2\left(x^2+2\right)-2\left(x^2+2\right)\)
\(=\left(x^2+2\right)\left(9x^2-2\right)\)
g: Ta có: \(-6x^2+5xy+4y^2\)
\(=-6x^2+8xy-3xy+4y^2\)
\(=-2x\left(3x-4y\right)-y\left(3x-4y\right)\)
\(=\left(3x-4y\right)\left(-2x-y\right)\)
h: Ta có: \(\left(x^2+4x\right)^2+8\left(x^2+4x\right)+15\)
\(=\left(x^2+4x\right)^2+3\left(x^2+4x\right)+5\left(x^2+4x\right)+15\)
\(=\left(x^2+4x+3\right)\cdot\left(x^2+4x+5\right)\)
\(=\left(x+1\right)\left(x+3\right)\left(x^2+4x+5\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Lời giải:
a)
$25+20x+4x^2=5^2+2.5.2x+(2x)^2=(5+2x)^2$
d)
$ab^2+\frac{1}{4}a^2b^4+1=(\frac{1}{2}ab^2)^2+2.\frac{1}{2}ab^2.1+1^2$
$=(\frac{1}{2}ab^2+1)^2$
b)
$a^2+9-6a=a^2-2.3a+3^2=(a-3)^2$
e)
$4x^4-4x^2+1=(2x^2)^2-2.2x^2+1^2=(2x^2-1)^2$
c)
$36a^2-60ab+25b^2=(6a)^2-2.6a.5b+(5b)^2=(6a-5b)^2$
f)
$9x^4+16y^6-24x^2y^3=(3x^2)^2-2.3x^2.4y^3+(4y^3)^2$
$=(3x^2-4y^3)^2$
\(36a^2-60ab+25b^2\)
\(=\left(6a\right)^2-2.6a.5b+\left(5b\right)^2\)
\(=\left(6a-5b\right)^2\)
(Nhớ k cho mình với nhé!)