Question

The two lines $lx+my=n$ and $l^{\prime }x+m^{\prime }y=n^{\prime }$ are perpendicular if

• A. ll'+mm'=0
• B. lm'+ml'
• C. lm+l'm'=0
• D. lm'+ml'=0

Answer 1

Answer: (A)

Product of slopes $=-1$
$\Rightarrow l{l}^{\prime \prime }+m{m}^{\prime }=0$