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Tess tried to solve the differential equation 
(dy)/(dx)=2xy-6x. This is her work:

(dy)/(dx)=2xy-6x
Step 1:

(dy)/(dx)=(y-3)2x
Step 2: 
quad int(1)/(y-3)dy=int2xdx
Step 3: 
quad ln |y-3|=x^(2)+C_(1)
Step 4: 
quade^(ln |y-3|)=e^(x^(2))+C_(1)
Step 5: 
quad|y-3|=e^(x^(2))+C_(1)
Step 6: 
quad y-3=+-e^(x^(2))+C_(2)
Step 7: 
quad y=+-e^(x^(2))+C
Is Tess's work correct? If not, what is her mistake?
Choose 1 answer:
(A) Tess's work is correct.
(B) Step 1 is incorrect. We're not allowed to factor an expression when solving differential equations.
(C) Step 4 is incorrect. The right-hand side of the equation should be 
e^(x^(2)+C_(1)).
(D) Step 7 is incorrect. Tess didn't account for adding 3 to the right side.

Tess tried to solve the differential equation dydx=2xy6x \frac{d y}{d x}=2 x y-6 x . This is her work:\newlinedydx=2xy6x \frac{d y}{d x}=2 x y-6 x \newlineStep 11: dydx=(y3)2x\quad \frac{d y}{d x}=(y-3) 2 x \newlineStep 22: 1y3dy=2xdx \quad \int \frac{1}{y-3} d y=\int 2 x d x \newlineStep 33: lny3=x2+C1 \quad \ln |y-3|=x^{2}+C_{1} \newlineStep 44: elny3=ex2+C1 \quad e^{\ln |y-3|}=e^{x^{2}}+C_{1} \newlineStep 55: y3=ex2+C1 \quad|y-3|=e^{x^{2}}+C_{1} \newlineStep 66: y3=±ex2+C2 \quad y-3= \pm e^{x^{2}}+C_{2} \newlineStep 77: y=±ex2+C \quad y= \pm e^{x^{2}}+C \newlineIs Tess's work correct? If not, what is her mistake?\newlineChoose 11 answer:\newline(A) Tess's work is correct.\newline(B) Step 11 is incorrect. We're not allowed to factor an expression when solving differential equations.\newline(C) Step 44 is incorrect. The right-hand side of the equation should be ex2+C1 e^{x^{2}+C_{1}} .\newline(D) Step 77 is incorrect. Tess didn't account for adding 33 to the right side.

Full solution

Q. Tess tried to solve the differential equation dydx=2xy6x \frac{d y}{d x}=2 x y-6 x . This is her work:\newlinedydx=2xy6x \frac{d y}{d x}=2 x y-6 x \newlineStep 11: dydx=(y3)2x\quad \frac{d y}{d x}=(y-3) 2 x \newlineStep 22: 1y3dy=2xdx \quad \int \frac{1}{y-3} d y=\int 2 x d x \newlineStep 33: lny3=x2+C1 \quad \ln |y-3|=x^{2}+C_{1} \newlineStep 44: elny3=ex2+C1 \quad e^{\ln |y-3|}=e^{x^{2}}+C_{1} \newlineStep 55: y3=ex2+C1 \quad|y-3|=e^{x^{2}}+C_{1} \newlineStep 66: y3=±ex2+C2 \quad y-3= \pm e^{x^{2}}+C_{2} \newlineStep 77: y=±ex2+C \quad y= \pm e^{x^{2}}+C \newlineIs Tess's work correct? If not, what is her mistake?\newlineChoose 11 answer:\newline(A) Tess's work is correct.\newline(B) Step 11 is incorrect. We're not allowed to factor an expression when solving differential equations.\newline(C) Step 44 is incorrect. The right-hand side of the equation should be ex2+C1 e^{x^{2}+C_{1}} .\newline(D) Step 77 is incorrect. Tess didn't account for adding 33 to the right side.
  1. Factorize right-hand side: Tess starts by factoring the right-hand side of the differential equation.\newlinedydx=2xy6x\frac{dy}{dx} = 2xy - 6x\newlinedydx=2x(y3)\frac{dy}{dx} = 2x(y - 3)\newlineThis is a correct step as factoring is allowed and can be useful in solving differential equations.
  2. Separate variables for integration: Tess separates the variables to each side of the equation to integrate.\newline1y3dy=2xdx\int\frac{1}{y-3}\,dy = \int 2x\,dx\newlineThis is a correct step in solving separable differential equations.
  3. Integrate both sides: Tess integrates both sides of the equation.\newlinelny3=x2+C1\ln|y-3| = x^2 + C_1\newlineThe integration is done correctly, with C1C_1 being the constant of integration for the right-hand side.
  4. Exponentiate to solve for y3y-3: Tess exponentiates both sides to solve for y3|y-3|.elny3=ex2+C1e^{\ln|y-3|} = e^{x^2 + C_1}This step is incorrect. The right-hand side should be exponentiated as a whole, including the constant C1C_1.

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