Math Problem Statement

By implicit differentiation, find the equation of the tangent line to the curve x^2 + 2xy^2 - y = 11 at the point (1, -2). Provide this equation in the form y = ax + b.

Solution

To solve the problem, let's proceed step-by-step using implicit differentiation for the given curve:

x2+2xy2y=11x^2 + 2xy^2 - y = 11

Step 1: Implicitly Differentiate with Respect to xx

We will differentiate both sides of the equation with respect to xx. Remember that when differentiating terms involving yy, we'll use the chain rule since yy is a function of xx:

ddx(x2+2xy2y)=ddx(11)\frac{d}{dx} \left( x^2 + 2xy^2 - y \right) = \frac{d}{dx} (11)

Breaking it down term by term:

  1. ddx(x2)=2x\frac{d}{dx}(x^2) = 2x
  2. For the term 2xy22xy^2, use the product rule: ddx(2xy2)=2(y2+2xydydx)\frac{d}{dx}(2xy^2) = 2 \cdot \left( y^2 + 2xy \cdot \frac{dy}{dx} \right)
  3. ddx(y)=dydx\frac{d}{dx}(-y) = -\frac{dy}{dx}
  4. The derivative of the constant 1111 is zero.

Substituting these into the equation: 2x+2(y2+2xydydx)dydx=02x + 2 \left( y^2 + 2xy \cdot \frac{dy}{dx} \right) - \frac{dy}{dx} = 0

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

Expanding the expression: 2x+2y2+4xydydxdydx=02x + 2y^2 + 4xy \cdot \frac{dy}{dx} - \frac{dy}{dx} = 0

Rearranging to isolate dydx\frac{dy}{dx}: 4xydydxdydx=2x2y24xy \cdot \frac{dy}{dx} - \frac{dy}{dx} = -2x - 2y^2 Factoring out dydx\frac{dy}{dx}: dydx(4xy1)=2x2y2\frac{dy}{dx} (4xy - 1) = -2x - 2y^2 dydx=2x2y24xy1\frac{dy}{dx} = \frac{-2x - 2y^2}{4xy - 1}

Step 3: Substitute the Point (1, -2)

Substitute x=1x = 1 and y=2y = -2 into the derivative: dydx=2(1)2(2)24(1)(2)1\frac{dy}{dx} = \frac{-2(1) - 2(-2)^2}{4(1)(-2) - 1} dydx=2881=109=109\frac{dy}{dx} = \frac{-2 - 8}{-8 - 1} = \frac{-10}{-9} = \frac{10}{9}

So, the slope of the tangent line at the point (1,2)(1, -2) is 109\frac{10}{9}.

Step 4: Find the Equation of the Tangent Line

The equation of the tangent line can be written as: yy1=m(xx1)y - y_1 = m(x - x_1) where m=109m = \frac{10}{9}, and (x1,y1)=(1,2)(x_1, y_1) = (1, -2).

Substituting these values: y+2=109(x1)y + 2 = \frac{10}{9}(x - 1)

Expanding this equation: y+2=109x109y + 2 = \frac{10}{9}x - \frac{10}{9} y=109x1092y = \frac{10}{9}x - \frac{10}{9} - 2 y=109x289y = \frac{10}{9}x - \frac{28}{9}

So, the equation of the tangent line in the form y=ax+by = ax + b is: y=109x289y = \frac{10}{9}x - \frac{28}{9}

Would you like more details or have any questions about this solution?

Here are five related questions you might find useful:

  1. How do you use the product rule for differentiation?
  2. What is the chain rule in differentiation, and when should it be used?
  3. What are implicit and explicit functions in calculus?
  4. How do you derive the slope of a curve at a given point?
  5. What is the process for converting a linear equation into slope-intercept form?

Tip: When using implicit differentiation, always remember to apply the chain rule to any terms involving functions of xx and yy.

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Math Problem Analysis

Mathematical Concepts

Implicit Differentiation
Tangent Line
Algebra

Formulas

Implicit differentiation: d/dx(f(x, y)) = d/dx(g(x, y))
Tangent line equation: y - y1 = m(x - x1)
Slope of the tangent: m = dy/dx

Theorems

Chain Rule
Product Rule

Suitable Grade Level

University Level Calculus