Rut gon cac bieu thuc sau:

\(\)a)\(A=\dfrac{xy^2-xz^2-y^3+yz^2}{x^2\left(z-y\right)+y^2\left(x-z\right)+z^2\left(y-x\right)}\)

b)\(B=\dfrac{x^3-y^3-z^3+3xyz}{\left(x+y\right)^2+\left(y+z\right)^2+\left(z-x\right)^2}\)

c)\(C=\dfrac{x^4\left(y^2-z^2\right)+y^4\left(z^2-x^2\right)+z^4\left(x^2-y^2\right)}{x^2\left(y-z\right)+y^2\left(z-x\right)+z^2\left(x-y\right)}\)

cho hinh thang ABCD(AB//CD),duong phan giac ngoai cua goc A va goc D cat nhau tai E,duong phan giac ngoai cua goc Bva gocC cat nhau tai F.CM:

a)EF//AB//CD

b)EF=nua chu vi cua hinh thang ABCD

cho ▲can ABC can tai A, M la trung diem cua BC,ke Mx // AC cat AB tai E,My//AB cat AC tai F.CM:

a)EF la duong trung binh cua ▲ABC

b)AM la trung truc cua EF

cho tu giac ABCD,duong phan giac cua goc A va goc D cat nhau o M,duong phan giac cua goc B va goc C cat nhau o N,biet goc AMD=90 do.CM:tu giac ABCD la hinh thang

cho BT:

A\(=\left(\dfrac{x-2}{x^2-1}-\dfrac{x+2}{x^2+2x+1}\right).\dfrac{x^4-2x^2+1}{2}\)

a) Rut gon A

b)tinh A khi \(x^2-3x+2=0\)

c)tim x de A nguyen

cho hinh thang ABCD vuong tai A va D.M la trung diem cua AD,ke MH vuong goc voi BC,biet goc BMH=90 do. CM: tu giac MBHD la hinh thang 

cho ▲ABC can tai A,BH va CK la 2 duong cao.CM: tu giac BCHK la hinh thang can