স্পর্শক ও অভিলম্ব বিষয়ক

If a variable tangent to the curve ;x2y=c3x^{2}y=c^{3} makes intercepts a, b on x-and y-axes, respectively, then the value of& ;a2ba^{2}b is

হানি নাটস

Given x2y=c3 x^{2} y=c^{3}

Let variable point is (x1,y1) \left(x_{1}, y_{1}\right) on the curve.

(x2)(dydx)+(2x)(y)=0x2(dydx)=2xydydx=2xyx2=2yx At (x1,y1)dydx=2y1x1 \begin{array}{l} \left(x^{2}\right)\left(\frac{d y}{d x}\right)+(2 x)(y)=0 \\ x^{2}\left(\frac{d y}{d x}\right)=-2 x y \Rightarrow \frac{d y}{d x}=\frac{-2 x y}{x^{2}}=\frac{-2 y}{x} \\ \text { At }\left(x_{1}, y_{1}\right) \Rightarrow \frac{d y}{d x}=\frac{-2 y_{1}}{x_{1}} \end{array}

Equation of tangent is,

yy1=2y1x1(xx1)yx12xy1=3x1y1 using x12y1=c3 \begin{array}{l} y-y_{1}=\frac{-2 y_{1}}{x_{1}}\left(x-x_{1}\right) \\ y x_{1}-2 x y_{1}=3 x_{1} y_{1} \\ \text { using } x_{1}^{2} y_{1}=c^{3} \end{array}

Equation of tangent becomes,

yx12+2c3xx1=3c3 y x_{1}^{2}+\frac{2 c^{3} x}{x_{1}}=3 c^{3}

x \therefore x -intercept is a=3x12 a=\frac{3 x_{1}}{2}

4 -intercept is b=3c3x12 b=\frac{3 c^{3}}{x_{1}^{2}}

a2b=(3x12)23c3x12=27c34 \therefore a^{2} b=\left(\frac{3 x_{1}}{2}\right)^{2} \frac{3 c^{3}}{x_{1}^{2}}=\frac{27 c^{3}}{4}

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