Geometryhard · Past Paper
The angle between the lines represented by ax^2 + 2hxy + by^2 = 0 is 90 degrees if:
Ah^2 = ab
Ba + b = 0
Ca = b
Dh = 0
✓ Correct Answer: B — a + b = 0
For the lines to be perpendicular, the sum of coefficients of x^2 and y^2 must be zero (a + b = 0).
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