1) Tìm a,b,c biết :
\(\frac{21x^2+4x-41}{\left(x+1\right)\left(x+2\right)+\left(x-3\right)}=\frac{a}{x+1}+\frac{b}{x+2}+\frac{c}{x-3}\)
2)
a) Tìm x,y,z biết :
\(\hept{\begin{cases}x+xy+y=1\\y+yz+z=3\\z+zx+x=7\end{cases}}\)
b) tìm x,y \(\in\)N* thỏa mãn
\(\frac{1}{x}+\frac{1}{y}=\frac{1}{3}+\frac{1}{xy}\)