স্পর্শক ও অভিলম্ব বিষয়ক

The curve for which the ratio of the length of the segment by any tangent on the YY-axis to the length of the radius vector is constant (K)(K), is

হানি নাটস

Slope of tangent at

p(x,y) on y=f(x)=dydxp(x,y) \begin{aligned} p(x, y) & \text { on } y=f(x) \\ = & \left.\frac{d y}{d x}\right|_{p(x, y)} \end{aligned}

Equation of tangent at P P

yyxx=dydxyy=dydx(xx) \begin{array}{l} \Rightarrow \quad \frac{y-y}{x-x}=\frac{d y}{d x} \\ \Rightarrow \quad y-y=\frac{d y}{d x}(x-x) \end{array}

for y y -intercept put x=0 x=0 ,

γ=yxdydx - (1)  \gamma=y-x \frac{d y}{d x} \text { - (1) }

Radius vector OP=x2+y2 \overline{O P}=\sqrt{x^{2}+y^{2}} ————-(2)

Given, yxdydxx2+y2=k \quad \frac{y-x \frac{d y}{d x}}{\sqrt{x^{2}+y^{2}}}=k

x2+y2yxdydx=k(x2+y2)[ Let y=vxdydx=v+]vxx[v+xdvdx]=kx1+v2xdvdx=k1+v2dv1+v2=kdxxln(v+1+v2)=klnx+lncv+1+v2=cxk \begin{aligned} & \sqrt{x^{2}+y^{2}} \\ \Rightarrow & y-x \frac{d y}{d x}=k\left(\sqrt{x^{2}+y^{2}}\right) \quad\left[\begin{array}{l} \text { Let } y=v x \\ \Rightarrow \frac{d y}{d x}=v+ \end{array}\right] \\ \Rightarrow & v x-x\left[v+x \frac{d v}{d x}\right]=k x \sqrt{1+v^{2}} \\ \Rightarrow & -x \frac{d v}{d x}=k \sqrt{1+v^{2}} \Rightarrow \int \frac{d v}{\sqrt{1+v^{2}}}=-k \int \frac{d x}{x} \\ \Rightarrow & \ln \left(v+\sqrt{1+v^{2}}\right)=-k \ln x+\ln c \\ \Rightarrow & v+\sqrt{1+v^{2}}=\frac{c}{x^{k}} \end{aligned}

substituting v=y/x v=y / x

yx+1+(yx)2=cxky+x2+y2x=cxkk1(y+x2+y2)xk1=c \begin{array}{l} \Rightarrow \frac{y}{x}+\sqrt{1+\left(\frac{y}{x}\right)^{2}}=\frac{c}{x^{k}} \\ \Rightarrow \frac{y+\sqrt{x^{2}+y^{2}}}{x}=\frac{c}{x^{k}}{ }^{k-1} \\ \Rightarrow\left(y+\sqrt{x^{2}+y^{2}}\right) x^{k-1}=c \end{array}

\therefore Hence, Option ( B B ) is the correct answer.

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