Question

9x² + hxy + y² = 0 represents pair of parallel straight lines, if h is ______.

Options

• ±3

• ±6

• ±8

• ±9

Answer 1

9x² + hxy + y² = 0 represents pair of parallel straight lines, if h is ±6.

Explanation:

Comparing the given equation with

Ax² + 2Hxy + By² = 0, we get

A= 9, B = 1 and H = `h/2`

Since the lines are parallel,

H² = AB

`therefore h^2/4 = 9(1)`

⇒ h² = 36

⇒ h = ±6