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Harold tried to find all the points on the curve given by 
xy^(2)-x^(2)y=-54 where the line tangent to the curve is horizontal. This is his solution:
Step 1: Finding an expression for 
(dy)/(dx).

(dy)/(dx)=(y(2x-y))/(x(2y-x))
Step 2: Forming a system of equations.

{[xy^(2)-x^(2)y=-54],[x(2y-x)=0],[y(2x-y)!=0]:}
Step 3: Solving the system.

(6,3)
Is Harold's solution correct? If not, at which step did he make a mistake?
Choose 1 answer:
(A) The solution is correct.
(B) Step 1 is incorrect.
(C) Step 2 is incorrect.
(D) Step 3 is incorrect.

Harold tried to find all the points on the curve given by xy2x2y=54 x y^{2}-x^{2} y=-54 where the line tangent to the curve is horizontal. This is his solution:\newlineStep 11: Finding an expression for dydx \frac{d y}{d x} .\newlinedydx=y(2xy)x(2yx) \frac{d y}{d x}=\frac{y(2 x-y)}{x(2 y-x)} \newlineStep 22: Forming a system of equations.\newline{xy2x2y=54x(2yx)=0y(2xy)0 \left\{\begin{array}{l} x y^{2}-x^{2} y=-54 \\ x(2 y-x)=0 \\ y(2 x-y) \neq 0 \end{array}\right. \newlineStep 33: Solving the system.\newline(6,3) (6,3) \newlineIs Harold's solution correct? If not, at which step did he make a mistake?\newlineChoose 11 answer:\newline(A) The solution is correct.\newline(B) Step 11 is incorrect.\newline(C) Step 22 is incorrect.\newline(D) Step 33 is incorrect.

Full solution

Q. Harold tried to find all the points on the curve given by xy2x2y=54 x y^{2}-x^{2} y=-54 where the line tangent to the curve is horizontal. This is his solution:\newlineStep 11: Finding an expression for dydx \frac{d y}{d x} .\newlinedydx=y(2xy)x(2yx) \frac{d y}{d x}=\frac{y(2 x-y)}{x(2 y-x)} \newlineStep 22: Forming a system of equations.\newline{xy2x2y=54x(2yx)=0y(2xy)0 \left\{\begin{array}{l} x y^{2}-x^{2} y=-54 \\ x(2 y-x)=0 \\ y(2 x-y) \neq 0 \end{array}\right. \newlineStep 33: Solving the system.\newline(6,3) (6,3) \newlineIs Harold's solution correct? If not, at which step did he make a mistake?\newlineChoose 11 answer:\newline(A) The solution is correct.\newline(B) Step 11 is incorrect.\newline(C) Step 22 is incorrect.\newline(D) Step 33 is incorrect.
  1. Finding Expression for (dy)/(dx)(dy)/(dx): Finding an expression for (dy)/(dx)(dy)/(dx). To find where the tangent line to the curve is horizontal, we need to find where the derivative (dy)/(dx)(dy)/(dx) is equal to zero. Harold's expression for (dy)/(dx)(dy)/(dx) is: (dy)/(dx)=y(2xy)x(2yx)(dy)/(dx) = \frac{y(2x-y)}{x(2y-x)} We need to verify this by differentiating the given equation xy2x2y=54xy^2 - x^2y = -54 implicitly with respect to xx. Differentiating both sides with respect to xx, we get: y2+2xydydx2xydydxx2dydx=0y^2 + 2xy\frac{dy}{dx} - 2xy\frac{dy}{dx} - x^2\frac{dy}{dx} = 0 Simplifying, we get: y2x2dydx=0y^2 - x^2\frac{dy}{dx} = 0 Solving for (dy/dx)(dy/dx), we get: (dy/dx)=y2x2(dy/dx) = \frac{y^2}{x^2} It seems that Harold's expression for (dy)/(dx)(dy)/(dx) is incorrect.

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