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(dy)/(dt)=3t and 
y(2)=3.
What is 
t when 
y=6 ?
Choose all answers that apply:
A 
t=-2
B 
t=sqrt6
c 
t=6
D 
t=-sqrt6
E 
t=2

dydt=3t \frac{d y}{d t}=3 t and y(2)=3 y(2)=3 .\newlineWhat is t t when y=6 y=6 ?\newlineChoose all answers that apply:\newline(A) t=2 t=-2 \newline(B) t=6 t=\sqrt{6} \newline(C) t=6 t=6 \newline(D) t=6 t=-\sqrt{6} \newline(E) t=2 t=2

Full solution

Q. dydt=3t \frac{d y}{d t}=3 t and y(2)=3 y(2)=3 .\newlineWhat is t t when y=6 y=6 ?\newlineChoose all answers that apply:\newline(A) t=2 t=-2 \newline(B) t=6 t=\sqrt{6} \newline(C) t=6 t=6 \newline(D) t=6 t=-\sqrt{6} \newline(E) t=2 t=2
  1. Integrate to find general solution: To solve for tt when yy equals 66, we first need to integrate the differential equation dydt=3t\frac{dy}{dt} = 3t to find the general solution for yy in terms of tt. We integrate 3t3t with respect to tt to get y(t)y(t). The integral of 3t3t dt is yy00, where yy11 is the constant of integration.
  2. Use initial condition to find CC: Next, we use the initial condition y(2)=3y(2) = 3 to find the value of the constant CC. We substitute t=2t = 2 and y=3y = 3 into the equation y(t)=32t2+Cy(t) = \frac{3}{2}t^2 + C. 3=32(2)2+C3 = \frac{3}{2}(2)^2 + C simplifies to 3=32(4)+C3 = \frac{3}{2}(4) + C.
  3. Determine particular solution: Solving for CC, we get 3=6+C3 = 6 + C, which means C=36=3C = 3 - 6 = -3. Now we have the particular solution y(t)=32t23y(t) = \frac{3}{2}t^2 - 3.
  4. Find tt when yy equals 66: We want to find the value of tt when yy equals 66. We set y(t)=6y(t) = 6 and solve for tt: 6=32t236 = \frac{3}{2}t^2 - 3.
  5. Isolate t in equation: Adding 33 to both sides of the equation, we get 6+3=(32)t26 + 3 = \left(\frac{3}{2}\right)t^2. This simplifies to 9=(32)t29 = \left(\frac{3}{2}\right)t^2.
  6. Solve for tt: To isolate t2t^2, we multiply both sides by 23\frac{2}{3}: (23)×9=t2\left(\frac{2}{3}\right) \times 9 = t^2. This simplifies to 6=t26 = t^2.
  7. Check validity of solutions: Taking the square root of both sides, we find that t=6t = \sqrt{6} or t=6t = -\sqrt{6}.
  8. Check validity of solutions: Taking the square root of both sides, we find that t=6t = \sqrt{6} or t=6t = -\sqrt{6}.We check the interval for tt given in the question prompt. Since we are not restricted by an interval for tt, both t=6t = \sqrt{6} and t=6t = -\sqrt{6} are valid solutions.

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