Straight LineHardBloom L3

Question

If the line $y = x$ is one of the angle bisector of the pair of lines $ax^{2} + 2hxy + by^{2} = 0$, then:

Options

A.$a + b = 0$
B.$a - b = 0$
C.$h = 0$
D.$a + 2b = 0$

Solution

Sol. [Key Concept: $y = x$ being an angle bisector of ${ax}^{2 + 2}hxy + {by}^{2 = 0}$ forces $a + b = 0$.]

Lines make complementary angles with $X$-axis $\Rightarrow m_{1}m_{2} = 1 \Rightarrow \frac{a}{b} = 1$

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