Math Problem Statement

Find dy/dx if x = a cos^3(t) and y = a sin^3(t).

Solution

To find dydx\frac{dy}{dx}, we can use parametric differentiation, as both xx and yy are given as functions of tt.

The equations are: x=acos3t,y=asin3tx = a \cos^3 t, \quad y = a \sin^3 t

Steps:

  1. Compute dxdt\frac{dx}{dt} and dydt\frac{dy}{dt}: dxdt=a3cos2t(sint)=3acos2tsint\frac{dx}{dt} = a \cdot 3 \cos^2 t (-\sin t) = -3a \cos^2 t \sin t dydt=a3sin2t(cost)=3asin2tcost\frac{dy}{dt} = a \cdot 3 \sin^2 t (\cos t) = 3a \sin^2 t \cos t

  2. Use the chain rule for parametric differentiation: dydx=dydtdxdt\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}}

    Substituting the values: dydx=3asin2tcost3acos2tsint\frac{dy}{dx} = \frac{3a \sin^2 t \cos t}{-3a \cos^2 t \sin t}

  3. Simplify: dydx=sin2tcostcos2tsint=sintcost=tant\frac{dy}{dx} = \frac{\sin^2 t \cos t}{-\cos^2 t \sin t} = -\frac{\sin t}{\cos t} = -\tan t

Final Answer:

dydx=tant\frac{dy}{dx} = -\tan t

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Math Problem Analysis

Mathematical Concepts

Parametric Differentiation
Trigonometric Functions
Chain Rule

Formulas

dx/dt = a * 3 * cos^2(t) * (-sin(t))
dy/dt = a * 3 * sin^2(t) * cos(t)
dy/dx = (dy/dt) / (dx/dt)

Theorems

Chain Rule for Parametric Equations

Suitable Grade Level

Grades 11-12 or College Level