PQR is a right-angled triangle with the right angle at Q and k being the length of the perpendicular from Q on PR. If l, m and n are the lengths of sides PQ, QR, and PR respectively, then which of the following holds true?

 PQR is a right-angled triangle with the right angle at Q and k being the length of the perpendicular from Q on PR. If l, m and n are the lengths of sides PQ, QR, and PR respectively, then which of the following holds true?

	A	$\frac{1}{k^2}=\frac{1}{l^2}-\frac{1}{m^2}$
	B	$\frac{1}{k^2}=\frac{1}{l^2}+\frac{1}{m^2}$
	C	$\frac{1}{k^2}=\frac{1}{m^2}-\frac{1}{l^2}$
	D	$\frac{1}{m^2}=\frac{1}{l^2}-\frac{2}{k^2}$

Solution : B