Math Problem Statement

Use implicit differentiation to find an equation of the tangent line to the curve at the given point: x^{2/3} + y^{2/3} = 4 at the point (-3√3, 1).

Solution

We are given the equation of an astroid:

x2/3+y2/3=4x^{2/3} + y^{2/3} = 4

We need to find the equation of the tangent line to this curve at the point (33,1)\left(-3\sqrt{3}, 1\right) using implicit differentiation.

Step 1: Differentiate the equation implicitly

Differentiate both sides of the given equation with respect to xx, keeping in mind that yy is a function of xx.

ddx(x2/3+y2/3)=ddx(4)\frac{d}{dx}\left(x^{2/3} + y^{2/3}\right) = \frac{d}{dx}(4)

On the left-hand side, apply the chain rule:

ddx(x2/3)=23x1/3\frac{d}{dx}(x^{2/3}) = \frac{2}{3}x^{-1/3} ddx(y2/3)=23y1/3dydx\frac{d}{dx}(y^{2/3}) = \frac{2}{3}y^{-1/3} \cdot \frac{dy}{dx}

Thus, the differentiated equation becomes:

23x1/3+23y1/3dydx=0\frac{2}{3}x^{-1/3} + \frac{2}{3}y^{-1/3} \cdot \frac{dy}{dx} = 0

Step 2: Solve for dydx\frac{dy}{dx}

Now solve this equation for dydx\frac{dy}{dx}:

23y1/3dydx=23x1/3\frac{2}{3}y^{-1/3} \cdot \frac{dy}{dx} = - \frac{2}{3}x^{-1/3}

Cancel out the 23\frac{2}{3} on both sides:

y1/3dydx=x1/3y^{-1/3} \cdot \frac{dy}{dx} = - x^{-1/3}

Now isolate dydx\frac{dy}{dx}:

dydx=x1/3y1/3\frac{dy}{dx} = - \frac{x^{-1/3}}{y^{-1/3}}

This simplifies to:

dydx=(xy)1/3\frac{dy}{dx} = - \left( \frac{x}{y} \right)^{1/3}

Step 3: Find the slope of the tangent line at the point (33,1)(-3\sqrt{3}, 1)

Substitute x=33x = -3\sqrt{3} and y=1y = 1 into the expression for dydx\frac{dy}{dx}:

dydx=(331)1/3=(33)1/3\frac{dy}{dx} = - \left( \frac{-3\sqrt{3}}{1} \right)^{1/3} = - \left( -3\sqrt{3} \right)^{1/3}

We need to simplify (33)1/3(-3\sqrt{3})^{1/3}, which is a complex operation. Let's approximate it step-by-step:

(33)1/31.9129(-3\sqrt{3})^{1/3} \approx -1.9129

Thus, the slope at the point (33,1)(-3\sqrt{3}, 1) is approximately:

dydx(1.9129)=1.9129\frac{dy}{dx} \approx -(-1.9129) = 1.9129

Step 4: Find the equation of the tangent line

Using the point-slope form of the equation of a line:

yy1=m(xx1)y - y_1 = m(x - x_1)

Substitute the point (33,1)(-3\sqrt{3}, 1) and the slope m1.9129m \approx 1.9129:

y1=1.9129(x+33)y - 1 = 1.9129(x + 3\sqrt{3})

This is the equation of the tangent line to the curve at the given point.


Would you like me to clarify any details or go deeper into any part of this problem?

Here are 5 related questions for further practice:

  1. How does implicit differentiation differ from explicit differentiation?
  2. What is the general method to differentiate an equation implicitly?
  3. How would the process change if we had a different exponent in the astroid equation?
  4. Can you find the normal line equation to this curve at the same point?
  5. How would you compute the slope if the point had complex coordinates?

Tip: Always check the differentiability of implicit functions at a point before finding the slope of the tangent line.

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Astroid Curve
Tangent Line

Formulas

Implicit differentiation formula for x^{n} and y^{n}: d/dx(x^n) = nx^{n-1}, d/dx(y^n) = ny^{n-1}(dy/dx)
Point-slope form for the tangent line: y - y1 = m(x - x1)

Theorems

Chain Rule
Slope of Tangent Line

Suitable Grade Level

Undergraduate Calculus