Chapter 30 - Quantum Physics - Problems and Conceptual Exercises - Page 1075: 51

$107^{\circ}$

We know that $\Delta \lambda=\frac{h}{mc}(1-cos\theta)$ We plug in the known values to obtain: $3.13\times 10^{-12}=\frac{6.63\times 10^{-34}}{9.1\times 10^{-31}\times 3\times 10^8}(1-cos\theta)$ $\implies 1.28=1-cos\theta$ $\implies \theta=107^{\circ}$