Rajasthan BoardEnglish MediumSTD 11 ScienceMATHSHyperbola5 Marks
Question
If P is any point on the hyperbola whose axis are equal, prove that SP . SP =$\text{CP}^{2}$
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Answer
For a hyperbola if the lenght of semi transverse and semi conjugate axes are equal. Then $\alpha\text{=b}$ Equation of the given hyperbola is $\text{x}^{2}-\text{y}^{2}=\alpha^{2}.....(1)$ Then e $=\sqrt{2}, \text{C}=(0, 0), S=(\sqrt{2\text{a}}, 0), S=(-\sqrt(\text{2a}, 0)$ Let coordinates of any point P on hyperbola be $ (\alpha, \beta). $ Since P lies on (1) ? $\alpha-\beta^{2}=\alpha^{2}......(2)$ Now $\text{SP}^{2}.\text{SP}^{2}$$=(2\alpha^{2}+\alpha^{2}+\beta^{2})^{2}-8\text{a}^{2}\alpha^{2}$ $=4\alpha^{4}+4\alpha^{2}(\alpha^{2}+\beta^{2})+(\alpha^{2}+\beta^{2})-8\text{a}^{2}\text{a}^{2}$ $=4\text{a}^{2}(\alpha^{2}-2\alpha^{2})+4\text{a}^{2}(\alpha^{2}+\beta^{2})+(\alpha^{2}+\beta^{2})^{2}$ $=4\alpha^{2}(\alpha^{2}-\beta^{2}-2\alpha^{2})+4\text{a}^{2}(\alpha^{2}+\beta^{2})+(\alpha^{2+}\beta^{2})^{2}$ $=(\alpha^{2}+\beta^{2})^{2}=\text{CP}^{4}$ $\text{SP. }\text{SP}=\text{CP}^{2}$
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