If (3a + 6b + c + 2d) × (3a − 6b − c + 2d) = (3a − 6b + c − 2d) × (3a + 6b − c − 2d), then which one of the following is correct?

LHS = ((3a+2d)+(6b+c))((3a+2d)−(6b+c)) = (3a+2d)²−(6b+c)². RHS = ((3a−2d)+(c−6b))((3a−2d)−(c−6b)) = (3a−2d)²−(c−6b)² = (3a−2d)²−(6b−c)². Difference: (3a+2d)²−(3a−2d)² = 24ad and (6b+c)²−(6b−c)² = 24bc. So 24ad = 24bc, ad = bc.