Question

If $a_1 ,b_1 ,c_1$ and $a_2 , b_2 ,c_2$ are the d.rs of two lines then $( a_1 a_2 + b_1 b_2 + c_1 c_2)^2 + \sum (b_1 c_2 - b_2 c_1)^2 =$

• A. $(a_1 + b_1 +c_1)(a_2 + b_2 +c_2)$
• B. $(a_1 b_1 c_1)(a_2 b_2 c_2)$
• C. 1
• D. $( a_1^2 + b_1^2 +c_1^2)(a_2^2 + b_2^2 + c^2_2 )$

Answer 1

Answer: (D)

$( a_1^2 + b_1^2 +c_1^2)(a_2^2 + b_2^2 + c^2_2 )$

Answer 2

Answer (d) $( a_1^2 + b_1^2 +c_1^2)(a_2^2 + b_2^2 + c^2_2 )$