If the system of equations $x+2y+3z=3,4x+3y-4z=4,8x+4y-\lambda z=9+\mu$  has infinitely many solutions, then the ordered pair $(\lambda ,\mu )$ is equal to

Use   $\Delta =0\&{\Delta }_3=0$

$\left|\begin{array}{ccc}1& 2& 3\\ 4& 3& -4\\ 8& 4& -\lambda \end{array}\right|=0\Rightarrow -3\lambda +16-2(-4\lambda +32)+3(16-24)=0$

$-3\lambda +16+8\lambda -64-24=0$

$5\lambda -72=0\Rightarrow \lambda =\frac{72}{5}$

$\left|\begin{array}{ccc}1& 2& 3\\ 4& 3& 4\\ 8& 4& 9+\mu \end{array}\right|=0\Rightarrow 27+3\mu -16-2(36+4\mu -32)+3(16-24)=0$

$-5\mu -21=0$

$\mu =\frac{-21}{5}$