2.1-8: ======= Solve y'=7y(y-13) with y(0)=17 Step 1. Identify as variables separable y'=F(x)G(y), with F=7, G=y(y-13). Step 2. Divide by G(y) and apply quadrature to get 7x+c on the right and a partial fraction integration problem on the left: | y'dx | int| ---------| = 7x+c | y(y-13) | 1 A B Step 3. Partial fractions ------ = --- + ------ y(y-13) y y - 13 Use a sampling method to solve for A=-/13, B=1/13. Step 4. Evaluate the constant c using y(0)=17. Step 5. Solve for y(x), the explicit solution. Use log and exponential rules and the trick | u | = +1 or -1 times u. Step 6. Answer check. The book answer is correct. The text also has a phase diagram drawn, which matches what you could do in two minutes from the phase line diagram method in class. See textbook section 2.2 for more info. 2.1-16: ======= The rabbit problem. Information in English in the problem statement implies P'=aP - bP^2, P(0)=120. The terms aP and bP^2, known as birth and death terms, are given at t=0: aP(0)=8, b(P(0))^2=6. Insert P(0)=120 to find a=1/15 and b=6/(120)^2. Let M=a/b=carrying capacity. Then M=160. Use the book formula in section 2.1 for P(t): M P(0) P(t)= ---------------------- P(0)+(M-P(0))exp(-a t) Fill in all the constants and then solve P(T)=0.95 M for T=15 ln(95/15).