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Calc 2 Final
| Question | Answer |
|---|---|
| What is a differential equation? | An equation involving an unknown function y(t) and its derivatives. It is relating a function and its derivative. |
| What is the difference between autonomous and pure time differential equations? | Pure time only involves time as a variable of the equation (example: dy/dt=g(t)). Autonomous involves y as a variable (example: dy/dt=g(y)) |
| What is meant by the 'order' of a differential equation? | It's how many derivatives we're taking |
| How does one tell if an autonomous DE is locally stable or unstable? | If the derivative is negative, it is locally stable. If it is positive, it is unstable. |
| What is the formula for Euler's Method? | y (sub n+1) = y (sub n) + h * [F(t (sub n), y (sub n))] where h= step size and F(t, y) = t+y |
| What is the Lotka-Volterra Equation that models a predator population, M (with the prey population represented by D)? | dM/dt= (-k*M)+(b*D*M), where (-k*M) represents the predator population decreasing if they don't feed, and (b*D*M) representing how feeding on prey increases the birth of new predators. |
| What is the Lotka-Volterra Equation that models a prey population, D (with the predator population represented by M?) | dD/dt= (r*D)-(a*D*M), where r is the rate of prey birth, and a is the rate at which they are eaten |
| What is the chain rule? | d/dx [f(g(x))] = f'(g(x)) * g'(x). AKA, f*g = f' * g + g' * f |
| What is a separable differential equation? | It is a DE of the form dy/dt= f(t) * g(y) |
| What are the steps for evaluating a separable differential equation, dy/dt= (some mess)? | 1.) multiply by dt and move t's to one side. 2.) Integrate both sides (remember c!) 3.) Solve for y. Now we have y= (an equation). Yay |
| How do we solve a separable equation with an initial condition (example: y(0)=5) | Once a separable equation has been turned from dy/dt=(mess) into y=(equation+c), if y(0)=5, then we plug in 5 for y and 0 for all of the t's in the equation, and solve for c. |
| What is the derivative of tan(x)? | sec^2(x) |
| What is the derivative of sec(x)? | sec(x)tan(x) |
| What is the derivative of cot(x)? | -csc^2(x) |
| What is the derivative of csc(x)? | csc(x)cot(x) |