Answer to Question #294828 in Calculus for Silvius

Question #294828

At any point (x, y) on a curve, 𝑑^2𝑦/𝑑π‘₯^2 = 1-x^2


, and an equation of the tangent line to the


curve at the point (1, 1) is y = 2 – x. Find an equation of the curve.

1
Expert's answer
2022-02-08T07:28:01-0500

Solution:

d2ydx2=1βˆ’x2β‡’dydx=xβˆ’x33+C\dfrac{d^2y}{dx^2}=1-x^2 \\\Rightarrow \dfrac{dy}{dx}=x-\dfrac{x^3}3+C

Given, tangent y=2–xy = 2 – x

So, slope of tangent =m=βˆ’1=m=-1

At (1, 1), m=dydxm=\dfrac{dy}{dx}

β‡’xβˆ’x33+C=mβ‡’1βˆ’13+C=βˆ’1β‡’C=βˆ’53\Rightarrow x-\dfrac{x^3}3+C=m \\\Rightarrow 1-\dfrac13+C=-1 \\ \Rightarrow C=-\dfrac53

So, dydx=xβˆ’x33βˆ’53\dfrac{dy}{dx}=x-\dfrac{x^3}3-\dfrac53

Also, at any point, m=dydxm=\dfrac{dy}{dx}

xβˆ’x33βˆ’53=βˆ’1β‡’x=βˆ’2,x=1x-\dfrac{x^3}3-\dfrac53=-1 \\ \Rightarrow x=-2,x=1

For x=βˆ’2:y=2βˆ’x=2+2=4x=-2: y=2-x=2+2=4

For x=1:y=2βˆ’x=2βˆ’1=1x=1:y=2-x=2-1=1

Points are (-2,4), (1,1).

Consider dydx=xβˆ’x33βˆ’53\dfrac{dy}{dx}=x-\dfrac{x^3}3-\dfrac53 again.

On integrating:

y=x2βˆ’x412βˆ’53x+C1y=x^2-\dfrac{x^4}{12}-\dfrac53x+C_1

Put (1,1) in this and solve for C1

1=1βˆ’112βˆ’53+C1β‡’C1=74∴y=x2βˆ’x412βˆ’53x+741=1-\dfrac{1}{12}-\dfrac53+C_1 \\\Rightarrow C_1=\dfrac74 \\ \therefore y=x^2-\dfrac{x^4}{12}-\dfrac53x+\dfrac74


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