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Prove that any hyperbola and its conjugate hyperbola cannot have common normal. |
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Answer» Consider hyperbola `(x^(2))/(a^(2))-(y^(2))/(b^(2))=1.` Equation of normal to hyperbola at point `P(a sec theta, b tan theta)` is `ax cos theta+by cot theta=a^(2)+b^(2)" (1)"` Equation of normal to hyperbola `(x^(2))/(a^(2))-(y^(2))/(b^(2))=-1` at point `Q( a tan phi, b sec phi)` is `ax cot phi+"by" cos phi=a^(2)+b^(2)" (2)"` If Eqs. (1) and (2) represent the same straight line, then `(cot phi)/(cos theta)=(cos phi)/(cot theta)=1` `rArr" "tan phi = sec theta and sec phi = tan theta` `rArr" "sec^(2)phi-tan^(2)phi=tan^(2)theta-sec^(2)theta=-1,` which is not possible. Thus, hyperbola and its conjugate hyperbola cannot have common normal. |
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