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A curve is defined by the parametric equations 
x(t)=-3cos(-t) and 
y(t)=5e^(-9t). Find 
(dy)/(dx).
Answer:

A curve is defined by the parametric equations x(t)=3cos(t) x(t)=-3 \cos (-t) and y(t)=5e9t y(t)=5 e^{-9 t} . Find dydx \frac{d y}{d x} .\newlineAnswer:

Full solution

Q. A curve is defined by the parametric equations x(t)=3cos(t) x(t)=-3 \cos (-t) and y(t)=5e9t y(t)=5 e^{-9 t} . Find dydx \frac{d y}{d x} .\newlineAnswer:
  1. Find dxdt\frac{dx}{dt}: To find dydx\frac{dy}{dx} for parametric equations, we need to find dydt\frac{dy}{dt} and dxdt\frac{dx}{dt} separately and then divide dydt\frac{dy}{dt} by dxdt\frac{dx}{dt}.
  2. Find dydt\frac{dy}{dt}: First, let's find dxdt\frac{dx}{dt}. The derivative of x(t)=3cos(t)x(t) = -3\cos(-t) with respect to tt is dxdt=3ddt[cos(t)]\frac{dx}{dt} = -3 \cdot \frac{d}{dt}[\cos(-t)]. Since the derivative of cos(u)\cos(u) with respect to uu is sin(u)-\sin(u), and using the chain rule with u=tu = -t, we get dxdt=3(sin(t))(1)=3sin(t)\frac{dx}{dt} = -3 \cdot (-\sin(-t)) \cdot (-1) = 3\sin(-t).
  3. Calculate dydx\frac{dy}{dx}: Now, let's find dydt\frac{dy}{dt}. The derivative of y(t)=5e9ty(t) = 5e^{-9t} with respect to tt is dydt=5ddt[e9t]\frac{dy}{dt} = 5 \cdot \frac{d}{dt}[e^{-9t}]. Since the derivative of eue^{u} with respect to uu is eue^{u}, and using the chain rule with u=9tu = -9t, we get dydt=5e9t(9)=45e9t\frac{dy}{dt} = 5 \cdot e^{-9t} \cdot (-9) = -45e^{-9t}.
  4. Simplify dydx\frac{dy}{dx}: To find dydx\frac{dy}{dx}, we divide dydt\frac{dy}{dt} by dxdt\frac{dx}{dt}. So, dydx=dydtdxdt=45e9t3sin(t)\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{-45e^{-9t}}{3\sin(-t)}.
  5. Simplify dydx\frac{dy}{dx}: To find dydx\frac{dy}{dx}, we divide dydt\frac{dy}{dt} by dxdt\frac{dx}{dt}. So, dydx=dydtdxdt=45e9t3sin(t)\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{-45e^{-9t}}{3\sin(-t)}.We can simplify the expression for dydx\frac{dy}{dx} by dividing both the numerator and the denominator by 33. This gives us dydx=45/3e9tsin(t)=15e9t/sin(t)\frac{dy}{dx} = \frac{-45/3e^{-9t}}{\sin(-t)} = -15e^{-9t} / \sin(-t).

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