1) Phan tich da thuc thanh nhan tu:
x3 - 4x2 - 12x + 27
2) Lam tinh chia:
(x2 - y2 + 6x + 9) : (x + y + 3)
3) CMR:
x - x2 - 1 <0 voi moi so thuc x
4) Tim x, biet:
x + 2V2 x2 + 2x3 = 0
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\(a,x^2+6x+9\)
\(=\left(x+3\right)^2\)
\(b,10x-25-x^2\)
\(=-\left(x^2-10x+25\right)\)
\(=-\left(x-5\right)^2\)
\(c,8x^3-\frac{1}{8}\)
\(=8x^3-\left(\frac{1}{2}\right)^3\)
\(=\left(8x-\frac{1}{2}\right)\left(64x^2+4x+\frac{1}{4}\right)\)
\(d,8x^3+12x^2+6xy^2+y^3\)
\(=2\left(4x^3+6x^2+3xy^2+\frac{1}{2}y^3\right)\)
hok tốt!
Lời giải:
$x^3-4x^2-12x+27$
$=(x^3+3x^2)-(7x^2+21x)+(9x+27)$
$=x^2(x+3)-7x(x+3)+9(x+3)$
$=(x+3)(x^2-7x+9)$
\(x^2-4x+4-y^2\)
\(=\left(x-2\right)^2-y^2\)
\(=\left(x-2-y\right)\left(x-2+y\right)\)
\(x^2-4x+4-y^2\)
\(=\left(x-2\right)^2-y^2\)
\(=\left(x-2-y\right)\left(x-2+y\right)\)
\(x^3-4x^2+12x-27\)
\(=x^3-3x^2-x^2+3x+9x-27\)
\(=x^2\left(x-3\right)-x\left(x-3\right)+9\left(x-3\right)\)
\(=\left(x-3\right)\left(x^2-x+9\right)\)
Giải:
a) \(3x^2y-6xy^2\)
\(=3xy\left(x-2y\right)\)
Vậy ...
b) \(\left(2x-a\right)x^2-\left(2x-a\right)y\)
\(=\left(2x-a\right)\left(x^2-y\right)\)
\(=\left(2x-a\right)\left(x-\sqrt{y}\right)\left(x+\sqrt{y}\right)\)
Vậy ...
c) \(25a^2-c^2\)
\(=\left(5a-c\right)\left(5a+c\right)\)
Vậy ...
d) \(4-36x+81x^2\)
\(=2^2-2.2.9x+\left(9x\right)^2\)
\(=\left(2-9x\right)^2\)
Vậy ...
e) \(\left(x+7\right)2-\left(2x-9\right)2\)
\(=2\left[\left(x+7\right)-\left(2x-9\right)\right]\)
\(=2\left(x+7-2x+9\right)\)
\(=2\left(16-x\right)\)
Vậy ...
f) \(x^2-6x+8\)
\(=x^2-6x+9-1\)
\(=\left(x-3\right)^2-1\)
\(=\left(x-4\right)\left(x-2\right)\)
Vậy ...