Let \(E\) be an open subset of \(\mathbb {R}^n\) containing \(x_0\) and assume that \(\mathbf {f}\) is a continuously differentiable function mapping \(E\) into \(\mathbb {R}^n\).
- Use the method of successive approximations to prove that the initial value problem \(x'=\mathbf {f}(x)\), \(x(0)=x_0\), has a unique solution on some interval \([-a,a]\), and give an estimate for \(a\).
- Indicate how the result in (a) can be used to prove a similar result for the nonautonomous case.