dung dinh nghia hai phan thuc bang nhau chung to rang
a] x^2y^3/5=7x^3y^4/35xy
b] x^3-4x/10-5x= -x^2-2x/5
bai 1 sbt toan 8 tap 1 trang 23
dung dinh nghia 2 phan thuc bang nhau chung minh cac dang thuc sau
a)x^2\5=7x^3y^4\35xy
b)x^2(x+2)\x(x+2)^2=x\x+2
d)x^3-x^4\10-5x=-x^2-2x\5
dung dinh nghia 2 phan thuc bang nhau chung minh cac phan thuc sau bang nhau
\(\frac{2-x}{2+x}=\frac{x^2-4x+4}{4-x^2}\)
\(\frac{x^3-9x}{15-5x}=\frac{-x^2-3x}{5}\)
Lời giải:
\(\frac{x^2-4x+4}{4-x^2}=\frac{x^2-2.2.x+2^2}{2^2-x^2}=\frac{(x-2)^2}{(2-x)(2+x)}=\frac{(2-x)^2}{(2-x)(2+x)}=\frac{2-x}{2+x}\) (đpcm)
\(\frac{x^3-9x}{15-5x}=\frac{x(x^2-9)}{5(3-x)}=\frac{x(x-3)(x+3)}{5(3-x)}=\frac{-x(3-x)(x+3)}{5(3-x)}=\frac{-x(x+3)}{5}=\frac{-x^2-3x}{5}\) (đpcm)
1.dùng định nghĩa hai pahn thức bằng nhau để CM phân thức sau bằng nhau
\(\dfrac{x^3-9x}{15-5x}=\dfrac{-x^2-3x}{5}\)
2.dung dinh nghia hai phan thuc bang nhau de tim A
\(\dfrac{4x^2-3x+7}{A}=\dfrac{4x-7}{2x+3}\)
Bài 1:
\(\dfrac{x^3-9x}{15-5x}=-\dfrac{x\left(x^2-9\right)}{5\left(x-3\right)}=\dfrac{-x\left(x-3\right)\left(x+3\right)}{5\left(x-3\right)}=\dfrac{-x\left(x+3\right)}{5}=\dfrac{-x^2-3x}{5}\)
Bài 2:
Sửa đề: \(\dfrac{4x^2-3x-7}{A}=\dfrac{4x-7}{2x+3}\)
\(\Leftrightarrow A=\dfrac{\left(4x^2-3x-7\right)\left(2x+3\right)}{4x-7}\)
\(=\dfrac{4x^2-7x+4x-7}{4x-7}\cdot\left(2x+3\right)\)
\(=\left(x+1\right)\left(2x+3\right)\)
1 thinh nhan
a(3x-x)(4x-5)-(4x-1)(3x-2)
b2x(6x-2)-3x(4x-1)
2dung dinh nghia phan thuc bang nhau ,chung minh
a)12x^2y/8xy=6x^2y^2/4xy^2
b)2(x-1)/6x=x^2-x/3x^2
2 ) dung dinh nghia phan thuc bang nhau , chung minh
a) 12x^2y/8xy=6x^2y^2
b)2(x-1)/6x=x^2-x/3x^2
1) tinh nhan
a)(3x -x)(4x-5)-(4x-1)(3x-2)
b2x(6x-2)-3x(4x-1)
2 dung dinh ngia phan thuc bang nhau,chung minh
a)12x^2/8xy=6x^2y^2/4xy^2
b)2(x-1)/6x=x^2-x/3x^2
giup dum minh voi thu la la cung nop roi do ban !
cho 2 da thuc A=7x^2y^3-6xy^4+5x^3y-1
B=-x^3y-7x^2y^3+5-xy^4
tinh 2A-B
\(2A-B=\left(7x^2y^3-6xy^4+5x^3y-1\right).2-\left(-x^3y-7x^2y^3-xy^4\right)\)
=>\(2A-B=\left(14x^2y^3-12xy^4+10x^3-2\right)-\left(-x^3y-7x^2y^3+5-xy^4\right)\)
=>\(2A-B=\left(phá\right)ngoặc\)
=>\(2A-B=\left(14x^2y^3-7x^2y^3\right)+\left(10x^3y+x^3y\right)-12xy^4-xy^2+\left(-2+5\right)\)
=>\(2A-B=7x^2y^3+11x^3y-12xy^4-xy^2+3\)
học giỏi
Thu gọn biểu thức a)x^2-4x(3x-4)+7x-5 b)7x(x^2-5)-3x^2y(xy-6y^2) c)(5x+4)(2x-7) d)4x(2x-3)-5x(x-2)+x^2(3-x)
a: Ta có: \(x^2-4x\left(3x-4\right)+7x-5\)
\(=x^2-12x^2+16x+7x-5\)
\(=-11x^2+23x-5\)
b: Ta có: \(7x\left(x^2-5\right)-3x^2y\left(xy-6y^2\right)\)
\(=7x^3-35x-3x^3y^2+18x^2y^3\)
c: Ta có: \(\left(5x+4\right)\left(2x-7\right)\)
\(=10x^2-35x+8x-28\)
\(=10x^2-27x-28\)
Phan tich thanh nhan tu ( bang ki thuat bo sung hang dang thuc):
x^2-4xy-x+3y^2+3y
x^2+4xy+2x+3y^2+6y
6x^2+xy-7x-2y^2+7y-5
6a^2-ab-2b^2+a+4b