bài 1: biểu thức là đơn thức:
\(\frac15x^2y;-13;-\frac16x^3y^7\)
bài 2:
1. \(\left(x^2-2yz+z^2\right)-\left(3yz-z^2+5x^2\right)\)
\(=x^2-2yz+z^2-3yz+z^2-5x^2\)
\(=-4x^2-5yz+2z^2\)
2. \(\left(x^2-2yz+z^2\right)+\left(3yz-z^2+5x^2\right)\)
\(=x^2-2yz+z^2+3yz-z^2+5x^2\)
\(=6x^2+yz\)
bài 3:
1. \(\left(5x+1\right)^2=25x^2+10x+1\)
2. \(\left(x+3\right)^3=x^3+9x^2+27x+27\)
bài 4:
1. \(4x^4-4x^2+1=\left(2x^2-1\right)^2\)
2. \(4x^2-12x+9=\left(2x-3\right)^2\)
3. \(1-10x+25x^2=\left(5-x\right)^2\)
4. \(x^4+81+18x^2=\left(x^2+9\right)^2\)
bài 4:
1. \(\left(x+1\right)^3-\left(x-4\right)\left(x+4\right)-x^3\)
\(=\left(x+1\right)^3-\left(x^2-16\right)-x^3\)
\(=\left(x^3+3x^2+3x+1\right)-x^2+16-x^3\)
\(=2x^2+3x+17\)
2. \(\left(x+2\right)^3-x\left(x+3\right)\left(x-3\right)-2x^2-8\)
\(=\left(x+2\right)^3-x\left(x^2-9\right)-12x^2-8\)
\(=\left(x^3+6x^2+12x+8\right)-\left(x^3-9x\right)-12x^2-8\)
\(=-6x^2+21x\)
Bài 10:
\(A=-5x^2-4x+1\)
\(=-5\left(x^2+\frac45x-\frac15\right)\)
\(=-5\left(x^2+2\cdot x\cdot\frac25+\frac{4}{25}-\frac{9}{25}\right)=-5\left(x+\frac25\right)^2+\frac95\le\frac95\forall x\)
\(\) Dấu '=' xảy ra khi \(x+\frac25=0\)
=>\(x=-\frac25\)
Bài 9:
1: \(\left(3x^2y^2+6x^2y^3-12xy\right):3xy\)
\(=\frac{3x^2y^2}{3xy}+\frac{6x^2y^3}{3xy}-\frac{12xy}{3xy}\)
\(=xy+2xy^2-4\)
2: \(\left(15x^3y^2-6x^2y-3x^2y^2\right):6x^2y\)
\(=\frac{15x^3y^2}{6x^2y}-\frac{6x^2y}{6x^2y}-\frac{3x^2y^2}{6x^2y}\)
\(=\frac52x-1-\frac12y\)
Bài 5:
1: \(2y\left(x+2\right)-3x-6\)
=2y(x+2)-3(x+2)
=(x+2)(2y-3)
2: \(3\left(x+4\right)-x^2-4x\)
=3(x+4)-x(x+4)
=(x+4)(3-x)
Bài 7:
a: \(A=\left(2x-1\right)\left(4x^2+2x+1\right)-7\left(x^3+1\right)\)
\(=8x^3-1-7x^3-7\)
\(=x^3-8\)
b: Thay x=-1/2 vào A, ta được:
\(A=\left(-\frac12\right)^3-8=-\frac18-8=-\frac{65}{8}\)
em cần giải gấp bài 3 chi tiết mọi người giúp em với ạ. Làm bài dưới dạng phân số ạ em cần gấp
