Howell Stuart
03/17/2024 · Primary School
Given: \( x^{3}-2 x y+y^{3}=5 x \), find \( \frac{d y}{d x} \) at \( (1,2) 4 \)
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Tutor-Verified Answer
Step-by-step Solution
To find \(\frac{dy}{dx}\) for the equation \(x^3 - 2xy + y^3 = 5x\) at the point \((1, 2)\), we will use implicit differentiation.
1. Differentiate both sides of the equation with respect to \(x\):
\[
\frac{d}{dx}(x^3) - \frac{d}{dx}(2xy) + \frac{d}{dx}(y^3) = \frac{d}{dx}(5x)
\]
2. Applying the differentiation rules:
- The derivative of \(x^3\) is \(3x^2\).
- For \(2xy\), we use the product rule: \(\frac{d}{dx}(2xy) = 2\left(x\frac{dy}{dx} + y\right)\).
- The derivative of \(y^3\) is \(3y^2\frac{dy}{dx}\).
- The derivative of \(5x\) is \(5\).
Putting it all together, we have:
\[
3x^2 - 2\left(x\frac{dy}{dx} + y\right) + 3y^2\frac{dy}{dx} = 5
\]
3. Simplifying the equation:
\[
3x^2 - 2x\frac{dy}{dx} - 2y + 3y^2\frac{dy}{dx} = 5
\]
4. Rearranging terms to isolate \(\frac{dy}{dx}\):
\[
(3y^2 - 2x)\frac{dy}{dx} = 5 - 3x^2 + 2y
\]
5. Solving for \(\frac{dy}{dx}\):
\[
\frac{dy}{dx} = \frac{5 - 3x^2 + 2y}{3y^2 - 2x}
\]
6. Now we will evaluate \(\frac{dy}{dx}\) at the point \((1, 2)\):
Substituting \(x = 1\) and \(y = 2\):
\[
\frac{dy}{dx} = \frac{5 - 3(1)^2 + 2(2)}{3(2)^2 - 2(1)}
\]
Calculating the numerator:
\[
5 - 3(1) + 4 = 5 - 3 + 4 = 6
\]
Calculating the denominator:
\[
3(4) - 2 = 12 - 2 = 10
\]
Thus, we have:
\[
\frac{dy}{dx} = \frac{6}{10} = \frac{3}{5}
\]
Therefore, the value of \(\frac{dy}{dx}\) at the point \((1, 2)\) is
\[
\boxed{\frac{3}{5}}.
\]
Quick Answer
The value of \(\frac{dy}{dx}\) at the point \((1, 2)\) is \(\frac{3}{5}\).
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