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find the value of \( a \) if \( a x^{2}+9 y^{2}-3 x+2 y-1=0 \) Reprents on a circle and find its radius. |
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Answer» Given equation is : ax2 + 9y2 - 3x + 2y -1 = 0 .....(1) Equation (1) is represent an equation of circle if coefficient of x2 = coefficient of y2. ∴ a = 9 then equation (1) represents an equation of circle. Then equation (1) becomes 9x2 + 9y2 - 3x + 2y -1 = 0 ⇒ x2 + y2 - \(\frac{3}{9}x\) + \(\frac{2}{9}y\) - \(\frac{1}{9}\) = 0 ⇒ x2 - \(\frac{3}{9}x\) + (\(\frac{3}{18}\))2 + y2 + \(\frac{2}{9}y\) + \((\frac{1}{9})^2\)- \(\frac{1}{9}\) - (\(\frac{3}{18}\))2 - \((\frac{1}{9})^2\) = 0 ⇒ (x - \(\frac{3}{18}\))2 + (y + \(\frac{1}{9}\))2 = \(\frac{36+9+4}{18^2}\) ⇒ (x - \(\frac{3}{18}\))2 + (y + \(\frac{1}{9}\))2 = \(\frac{49}{18^2}\) = \((\frac{7}{18})^2\) ∴ Radius of the formed circle is \(\frac{7}{18}\). |
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