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For what value of k, the following pair of lines –kx + 2y + 3 = 0 and 2x + 4y + 7 = 0 are perpendicular ?
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- k = 2
- k = 4
- k = –1
- k = 3
Correct Option: B
When two lines are perpendicular than the product of their slopes is –1.
i.e m1 × m2 = –1
For equation
– kx + 2y + 3 = 0
| m2 = | |
| 2 |
k 1 2 = For equation 2x + 4y + 7 = 0
| m2 = - | |
| 4 |
| m2 = - | |
| 2 |
As lines are perpendicular
m1 × m2 = –1
| × - | = - 1 | ||
| 2 | 2 |
k = 4
