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Question
Math
Posted 10 months ago
The differentiable functions xx and yy are related by the following equation:
y2=x25
y^{2}=x^{2}-5


Also, dydt=2.1\frac{d y}{d t}=2.1.
Find dxdt\frac{d x}{d t} when y=2y=-2 and x>0x>0.
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
Differentiate both sides of the equation y2=x25y^2 = x^2 - 5 with respect to tt using the chain rule
step 2
Applying the chain rule gives 2ydydt=2xdxdt2y \frac{dy}{dt} = 2x \frac{dx}{dt}
step 3
Solve for dxdt\frac{dx}{dt} by dividing both sides by 2x2x, yielding dxdt=yxdydt\frac{dx}{dt} = \frac{y}{x} \frac{dy}{dt}
step 4
Substitute y=2y = -2 and dydt=2.1\frac{dy}{dt} = 2.1 into the equation from step 3
step 5
Since x>0x > 0 and y2=x25y^2 = x^2 - 5, we find xx by solving (2)2=x25(-2)^2 = x^2 - 5
step 6
Solving for xx gives x2=4+5x^2 = 4 + 5, so x=9=3x = \sqrt{9} = 3
step 7
Substitute x=3x = 3 into the equation from step 3 to find dxdt=232.1\frac{dx}{dt} = \frac{-2}{3} \cdot 2.1
step 8
Calculate dxdt=232.1=1.4\frac{dx}{dt} = \frac{-2}{3} \cdot 2.1 = -1.4
Answer
dxdt=1.4\frac{dx}{dt} = -1.4 when y=2y = -2 and x>0x > 0.
Key Concept
Implicit Differentiation and Chain Rule
Explanation
To find dxdt\frac{dx}{dt}, we use implicit differentiation on the given equation with respect to tt, and then solve for dxdt\frac{dx}{dt} using the given values for yy and dydt\frac{dy}{dt}.

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