N
nguyenhao1991


1)giai he pt
y(x^2-y^2)=3x
x(x^2+y^2)=10y
2)cho tam giac ABC
b/cosB+c/cosC+a/cosA=a/sinAsinC
cmr tam giac ABC vuong
y(x^2-y^2)=3x
x(x^2+y^2)=10y
2)cho tam giac ABC
b/cosB+c/cosC+a/cosA=a/sinAsinC
cmr tam giac ABC vuong