Add hint to problem

src/7_differential_equations_1.md

@@ -812,6 +812,8 @@ since we have demonstrated that $\vec{\phi}_{k}(t)$ is a solution of the DE.
 
     (b) $\dot{x(t)}=\frac{1}{3} x^2+3$, subject to $x(0)=3$.
 
+    Hint: it is fine if you use a computer algebra program to solve the integrals for these problems.
+
 4. [:smirk:] Solve the following equation and list all possible solutions
 
     $$\dot{x}=\cos^2(x)$$