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​Let k be a positive integer. Consider the differential equation{dydt=5ky5k+2,for t>0,y(0)=0Which
Question

Let k be a positive integer. Consider the differential equation{dydt=5ky5k+2,for t>0,y(0)=0Which of the following statements is true?\text{Let } k \text{ be a positive integer. Consider the differential equation} \\\begin{cases} \frac{dy}{dt} = \frac{5k}{y^{5k+2}}, & \text{for } t > 0, \\y(0) = 0 \end{cases} \\\text{Which of the following statements is true?}​​

A.

It has a unique solution which is continuously differentiable on (0,)(0,\infty)​ .

B.

It has at most two solutions which are continuously differentiable on (0,)(0,\infty)​​

C.

It has infinitely many solutions which are continuously differentiable on (0,)(0,\infty)​ .

D.

It has no continuously differentiable solutions on (0,)(0,\infty)​​

Correct option is C

​​dydt=y5k5k+2,for t>0y5k5k+2 dy=dt y15k5k+215k5k+2=t+C,y15k5k+2=(15k5k+2)(t+C)y25k+2=25k+2(t+C)y=[25k+2(t+C)]5k+22Using the initial condition: y(0)=0  C=0Hence, the solution becomes:y=[25k+2t]5k+22,for t>0Checking continuity and uniqueness:For t=0, y=0.For t>0,y=[25k+2t]5k+22.Now, Cauchy problem has 3 choices:1.No solution (not possible)2.Unique solution (not possible, as we have another solution)3.Infinitely many solutions (true)Since y is continuous, the correct statement is:It has infinitely many solutions which is continuously differentiable on(0,)\frac{dy}{dt} = y^\frac{5k}{5k+2}, \quad \text{for } t > 0 \\\int y^\frac{5k}{5k+2} \, dy = \int dt \\\ \frac{y^{1-\frac{5k}{5k+2}}}{1-\frac{5k}{5k+2}}= t + C, \\ y^{1-\frac{5k}{5k+2}} = (1-\frac{5k}{5k+2})(t + C) \\y^{\frac{2}{5k+2}} = \frac{2}{5k+2}(t+C) \\y=\big[\frac{2}{5k+2}(t+C)\big]^{\frac{5k+2}{2}}\\\text{Using the initial condition: }\\ y(0) = 0 \ \implies C=0\\\text{Hence, the solution becomes:} \\y=\big[\frac{2}{5k+2}t\big]^{\frac{5k+2}{2}}, \quad \text{for } t > 0 \\\text{Checking continuity and uniqueness:} \\\text{For } t = 0, \; y = 0. \\\text{For } t > 0 , y=\big[\frac{2}{5k+2}t\big]^{\frac{5k+2}{2}}. \\\text{Now, Cauchy problem has 3 choices:} \\1. \text{No solution (not possible)} \\2. \text{Unique solution (not possible, as we have another solution)} \\3. \text{Infinitely many solutions (true)} \\\text{Since } y \text{ is continuous, the correct statement is:} \\\textbf{It has infinitely many solutions which is continuously differentiable on}(0,\infty)​​

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