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252 - 152
= (25 - 15)(25 + 15)
= 10 . 40
= 400
2052 - 952
= (205 - 95)(205 + 95)
= 110 . 300
= 33 000
362 - 142
= (36 - 14)(36 + 14)
= 22 . 50
= 1 100
9502 - 8502
= (950 - 850)(950 + 850)
= 100 . 1 800
= 180 000
A= x3- 9x2+ 27x- 27 tại x=13, ta có:
A= 133- 9.132+ 27.13- 27
A= 133- 3.3.132+ 3.33.13- 33
A= (13- 3)3
A= 103
A= 1000
Vậy đa thức A tại x= 13 có kết quả bằng 1000
`A = x^3 - 9x^2 +27x - 27`
`->A = x^3 - 3 . x^2 . 3 + 3 . x . 3^2 -3^3`
`->A = (x-3)^3`
`->A = (13-3)^3`
`->A=10^3=10 000`
Vậy `A=10 000`
\(\left(x-2\right)^3-1=\left(x-2\right)\left[\left(x-3\right)^2+x-2\right]=\left(x-2\right)\left(x^2+5x+7\right)\)
\(\left(x+3y\right)^2-9y^2=x\left(x+6y\right)\)
\(\left(x+3\right)^2-\left(x-1\right)^2=4\left(2x+4\right)=8\left(x+2\right)\)
a) \(\left(x-2\right)^3-1=\left(x-2\right)^3-1^3=\left(x-2-1\right)\left[\left(x-2\right)^2+\left(x-2\right)\cdot1+1^2\right]\)\(=\left(x-3\right)\left(x^2-4x+4+x-2+1\right)\)
\(=\left(x-3\right)\left(x^2-3x+3\right)\)
b) \(\left(x+3y\right)^2-9y^2\)
\(=\left(x+3y\right)^2-\left(3y\right)^2\)
\(=\left(x+3y+3y\right)\left(x+3y-3y\right)\)
\(=x\left(x+6y\right)\)
c) \(\left(x+3\right)^2-\left(x-1\right)^2\)
\(=\left(x+3-x+1\right)\left(x+3+x-1\right)\)
\(=4\left(2x+2\right)\)
\(=8\left(x+1\right)\)
a) =(a-b-c +a-b+c)( a-b-c -a+b-c)
= 2(a-b)(-2c)= -4c(a-b)
làm tặng câu a) thui
\(\left(a-b-c\right)^2-\left(a-b+c\right)^2\)
\(=\left(a-b-c-a+b-c\right)\left(a-b-c+a-b+c\right)\)
\(=\left(-2c\right)\left(-2b+2a\right)\)
\(=2\left(a-b\right)\left(-2c\right)\)
\(=-4c\left(a-b\right)\)
a)\(-25+4x^2=\left(2x-5\right)\left(2x+5\right)\)
b)\(-x^2+10x-25=-\left(x^2-10x+25\right)=-\left(x-5\right)^2\)
c)\(\frac{1}{9}x^2+\frac{2}{3}xy+y^2=\left(\frac{1}{3}x+y\right)^2\)
\(a,-25+4x^2=4x^2-25=\left(2x-5\right)\left(2x+5\right)\)
\(b,-x^2+10x-25=-\left(x^2-10x+25\right)=-\left(x-5\right)^2\)
\(c,\frac{1}{9}x^2+\frac{2}{3}xy+y^2=\left(\frac{1}{3}x\right)^2+\frac{2.1}{3}xy+y^2=\left(\frac{1}{3}x+y\right)^2\)(sửa đề)
cau 1 \(x^2+6xy+9y^2=\left(x+3y\right)^2\)( binh phuong cua mot tong)
\(x^2-10xy+25y^2=\left(x-5y\right)^2\)( binh phuong cua mot hieu )
a, \(\left(4x+5\right)^2=\left(4x+5\right)\left(4x+5\right)=\left[\left(4x+5\right)4x\right]+\left[\left(4x+5\right)5\right]=4x^2+20x+25\)
b, \(\left(5x-2\right)^2=\left(5x-2\right)\left(5x-2\right)=\left[\left(5x-2\right)5x-\left(5x-2\right)2\right]=5x^2-10x+25\)
b, \(8^2-12x^2=\left(8^2-12x^2\right)\left(8^2+12x^2\right)\)
đúng ko :)
@No name: Bị sai rồi nhé, a,b,c sai hết :>
a) ( 4x + 5 )2
= ( 4x )2 + 2.4x.5 + 52
= 16x2 + 40x + 25
b) ( 5x - 2 )2
= ( 5x )2 - 2.5x.2 + 22
= 25x2 - 20x + 4
c) 82 - 12x2
= 64 - 12x2
= ( V8 - V12x )( V8 + V12x )