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Let 
x^(2)-y^(2)=28.
What is the value of 
(d^(2)y)/(dx^(2)) at the point 
(8,-6) ?
Give an exact number.

Let x2y2=28 x^{2}-y^{2}=28 .\newlineWhat is the value of d2ydx2 \frac{d^{2} y}{d x^{2}} at the point (8,6) (8,-6) ?\newlineGive an exact number.

Full solution

Q. Let x2y2=28 x^{2}-y^{2}=28 .\newlineWhat is the value of d2ydx2 \frac{d^{2} y}{d x^{2}} at the point (8,6) (8,-6) ?\newlineGive an exact number.
  1. Differentiate Once: We are given the equation x2y2=28x^{2} - y^{2} = 28. To find d2ydx2\frac{d^{2}y}{dx^{2}}, we need to differentiate the equation with respect to xx twice.\newlineFirst, let's differentiate the equation once with respect to xx.\newlineUsing the chain rule, the derivative of x2x^{2} with respect to xx is 2x2x, and the derivative of y2y^{2} with respect to xx is 2ydydx2y\frac{dy}{dx}.\newlineSo, the first derivative of the equation is:\newlined2ydx2\frac{d^{2}y}{dx^{2}}00
  2. Solve for dydx\frac{dy}{dx}: Now, we need to solve for dydx\frac{dy}{dx}. Rearrange the equation to isolate dydx\frac{dy}{dx}: 2y(dydx)=2x2y\left(\frac{dy}{dx}\right) = 2x dydx=2x2y\frac{dy}{dx} = \frac{2x}{2y} dydx=xy\frac{dy}{dx} = \frac{x}{y}
  3. Differentiate Again: Next, we differentiate the equation again with respect to xx to find the second derivative, d2ydx2\frac{d^2y}{dx^2}. Differentiating xy\frac{x}{y} with respect to xx using the quotient rule, which is v(dudx)u(dvdx)v2\frac{v\left(\frac{du}{dx}\right) - u\left(\frac{dv}{dx}\right)}{v^2}, where u=xu = x and v=yv = y, we get: d2ydx2=y(1)x(dydx)y2\frac{d^2y}{dx^2} = \frac{y(1) - x\left(\frac{dy}{dx}\right)}{y^2}
  4. Substitute dydx\frac{dy}{dx}: We already found that dydx=xy\frac{dy}{dx} = \frac{x}{y}, so we substitute this into our expression for the second derivative:\newlined2ydx2=yx(xy)y2\frac{d^2y}{dx^2} = \frac{y - x\left(\frac{x}{y}\right)}{y^2}\newlined2ydx2=yx2yy2\frac{d^2y}{dx^2} = \frac{y - \frac{x^2}{y}}{y^2}
  5. Simplify Expression: Now we simplify the expression:\newlined2ydx2=y2x2y3\frac{d^2y}{dx^2} = \frac{y^2 - x^2}{y^3}\newlineSince we know from the original equation that x2y2=28x^2 - y^2 = 28, we can rewrite y2x2y^2 - x^2 as 28-28.\newlined2ydx2=28y3\frac{d^2y}{dx^2} = \frac{-28}{y^3}
  6. Substitute Point: Finally, we substitute the given point (8,6)(8, -6) into the expression to find the exact value of the second derivative at that point.\newlined2ydx2=28(6)3\frac{d^2y}{dx^2} = \frac{-28}{(-6)^3}\newlined2ydx2=28216\frac{d^2y}{dx^2} = \frac{-28}{-216}\newlined2ydx2=28216\frac{d^2y}{dx^2} = \frac{28}{216}
  7. Final Answer: Simplify the fraction to get the final answer: d2ydx2=17.7\frac{d^{2}y}{dx^{2}} = \frac{1}{7.7}

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