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If a tangent of slope 2 of the ellipse `(x^2)/(a^2)+(y^2)/(b^2)=1`is normal to the circle `x^2+y^2+4x+1=0`, then the maximum value of `a b`is4 (b) 2(c) 1 (d)none of theseA. 4B. 2C. 1D. none of these |
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Answer» A tangent of slopw 2 to the ellipse `(x^(2))/(a^(2))+(y^(2))/(b^(2))=1` is `y==4x+-sqrt(4a^(2)+b^(2))" "(1)` This is normal to the circle `x^(2)+y^(2)+4x+1=0` Therefore, (1) passes througj (-2,0), i.e., or `0=-4+-sqrt(4a^(2)+b^(2))` or `4a^(2)+b^(2)=16` Using `AMgeGM`, we get `(4a^(2)+b^(2))/(2)gesqrt(4a^(2)-b^(2))` or `able4` |
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