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Review 6. Infinite integrals – rules U-substitution Slope Fields Separation of Variables. Change tanu to: And do a u-substitution for cosu. Change cotu to: And do a u-substitution for sinu:. Change. Change. U-Substitution.
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Review 6 • Infinite integrals – rules • U-substitution • Slope Fields • Separation of Variables
Change tanu to: • And do a u-substitution for cosu
Change cotu to: • And do a u-substitution for sinu:
U-Substitution • You replace the part that cannot be integrated – it’s a composition function. The inside gets replaced. • Take the derivative of the u with respect to x. This needs to match what is left in the original integral. You can only differ by a constant! • If there are limits, then you need to adjust the limits in terms of the u, then integrate and evaluate.
examples Missing constant of 3, so divide the 3 to the other side to du
Examples The quantity to the 5th power is u Matches exactly
Examples Tan is the issue since it is raised to a power and its derivative is sec squared. No 4 present so divide it to the du
Limits with u-sub examples Change the limits to terms of u Evaluate Stop here unless a mc question
examples Replace the limits with respect to u Done unless a mc question
Slope fields • Slope fields are mapping every possible tangent line for a function that is offset by a different constant c.
Create the slope field for dy/dx=xy Show calculations for the slope fields on a free response question
Create the slope field for dy/dx = 1/(x+1) Show calculations for the slope fields on a free response question
Separation of variables. • Relocate the y to the side with dy, the dx to the side with dx. • Integrate both sides, remembering to include the constant c on the x side. • Find c now! It’s in an easier format. • Write the solution in terms of y = • you might have to take into consideration the initial condition (to find c) where it either lies or what the slope at that point is to determine the sign associated with the final answer. (only if you have to remove an absolute value or if you have square rooted the equation).
Solve dy/dx=xy for the initial condition of (2,1) Find c first, then e both sides Since the solution is at (2, 1) and the slope is positive, you can drop the absolute value.
Solve the differential equation of dy/dx = 1/(x+1) with the initial condition of (0, 2) Technically, you should do a u-sub for x+1 Find c