If the equation of the pair of straight lines intersecting at ( $a, b$ ) and perpendicular to the pair of lines $3 x^2-4 x y+5 y^2=0$ is $l x^2+2 n x y+m y^2-32 x-26 y+c=0$, then $\frac{a+b+c}{l+h+m}=$

$P Q R$ is a right-angled isosceles triangle with right angle at $P(2,1)$. If the equation of the line $Q R$ is $2 x+y=3$, then the equation representing the pair of lines $P Q$ and $P R$ is

The coordinate axes are rotated about the origin in the counter clockwise direction through an angle $60^{\circ}$. If a and $b$ are the intercepts made on the new axes by a straight line whose equation referred to the original axes is $x+y=1$, then $\frac{1}{a^2}+\frac{1}{b^2}=$

The image of a point $(2,-1)$ with respect to the line $x-y+1=0$ is