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A curve is defined by the parametric equations 
x(t)=-7cos(-6t) and 
y(t)=9sin(6t). Find 
(dy)/(dx).
Answer:

A curve is defined by the parametric equations x(t)=7cos(6t) x(t)=-7 \cos (-6 t) and y(t)=9sin(6t) y(t)=9 \sin (6 t) . Find dydx \frac{d y}{d x} .\newlineAnswer:

Full solution

Q. A curve is defined by the parametric equations x(t)=7cos(6t) x(t)=-7 \cos (-6 t) and y(t)=9sin(6t) y(t)=9 \sin (6 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, we find dxdt\frac{dx}{dt}. The derivative of x(t)=7cos(6t)x(t) = -7\cos(-6t) with respect to tt is dxdt=7×6sin(6t)\frac{dx}{dt} = -7 \times 6\sin(-6t) because the derivative of cos(u)\cos(u) with respect to uu is sin(u)-\sin(u) and we apply the chain rule with u=6tu = -6t.
    dxdt=7×6sin(6t)=42sin(6t)\frac{dx}{dt} = -7 \times 6\sin(-6t) = 42\sin(-6t)
  3. Calculate dydx\frac{dy}{dx}: Next, we find dydt\frac{dy}{dt}. The derivative of y(t)=9sin(6t)y(t) = 9\sin(6t) with respect to tt is dydt=9×6cos(6t)\frac{dy}{dt} = 9 \times 6\cos(6t) because the derivative of sin(u)\sin(u) with respect to uu is cos(u)\cos(u) and we apply the chain rule with u=6tu = 6t.
    dydt=9×6cos(6t)=54cos(6t)\frac{dy}{dt} = 9 \times 6\cos(6t) = 54\cos(6t)
  4. Simplify fraction: Now we divide dydt\frac{dy}{dt} by dxdt\frac{dx}{dt} to find dydx\frac{dy}{dx}.dydx=dydtdxdt=54cos(6t)42sin(6t)\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{54\cos(6t)}{42\sin(-6t)}
  5. Final result: We can simplify the fraction by dividing both the numerator and the denominator by 66. \newlinedydx=(546cos(6t))(426sin(6t))=(9cos(6t))(7sin(6t))\frac{dy}{dx} = \frac{(\frac{54}{6} \cdot \cos(6t))}{(\frac{42}{6} \cdot \sin(-6t))} = \frac{(9\cos(6t))}{(7\sin(-6t))}
  6. Final result: We can simplify the fraction by dividing both the numerator and the denominator by 66. \newlinedydx=(54/6cos(6t))(42/6sin(6t))=(9cos(6t))(7sin(6t))\frac{dy}{dx} = \frac{(54/6 \cdot \cos(6t))}{(42/6 \cdot \sin(-6t))} = \frac{(9\cos(6t))}{(7\sin(-6t))}Since sin(θ)=sin(θ)\sin(-\theta) = -\sin(\theta), we can simplify the denominator to sin(6t)-\sin(6t). \newlinedydx=(9cos(6t))(7sin(6t))=9cos(6t)7sin(6t)\frac{dy}{dx} = \frac{(9\cos(6t))}{(7 \cdot -\sin(6t))} = -\frac{9\cos(6t)}{7\sin(6t)}

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