If the quadratic equations $3x^2+ax+1=0$ and $2x^2+bx+1=0$ have a common root, then the value of the expression $5ab-2a^2-3b^2$ is 

$6x^2+2ax+2=0$ and $6x^2+3bx+3=0$  
Subtracting $x(2a-3b)-1=0$  
$\Rightarrow x=\frac{1}{2a-3b}$ (put in any equation)
$=\frac{1}{{(2a-3b)}^2}+\frac{b}{2a-3b}+1=0$ 
$2+b(2a-3b)+{(2a-3b)}^2=0$ 
$4a^2+9b^2-12ab+2ab-3b^2+2=0$ 
$-10ab+6b^2+4a^2+1=0$