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Question 130 of 139

Q.If angle between the lines represented by ax2+2hxy+by2=0ax^2+2hxy+by^2=0 is equal to the angle between the lines represented by 2x2−5xy+3y2=02x^2-5xy+3y^2=0, then show that 100(h2−ab)=(a+b)2100(h^2-ab)=(a+b)^2.

Maharashtra MsbshseMaharashtra HSC (MSBSHSE) Board 2022Subjective· 3mImportance★★★★★
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Equate tan⁡θ\tan\theta for the given pair with tan⁡θ\tan\theta of 2x2−5xy+3y2=02x^2-5xy+3y^2=0.

For ax2+2hxy+by2=0ax^2+2hxy+by^2=0: tan⁡θ=∣2h2−aba+b∣\tan\theta = \left|\dfrac{2\sqrt{h^2-ab}}{a+b}\right|

For 2x2−5xy+3y2=02x^2-5xy+3y^2=0: a′=2, 2h′=−5⇒h′=−52, b′=3a'=2,\ 2h'=-5\Rightarrow h'=-\dfrac52,\ b'=3

tan⁡θ′=∣2(h′)2−a′b′a′+b′∣=∣2254−65∣=∣2145∣=2⋅125=15\tan\theta' = \left|\dfrac{2\sqrt{(h')^2-a'b'}}{a'+b'}\right| = \left|\dfrac{2\sqrt{\frac{25}4-6}}5\right| = \left|\dfrac{2\sqrt{\frac14}}5\right| = \dfrac{2\cdot\frac12}5 = \dfrac15

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