[填空题]
What would be the wavelengths of the two phesz 2 6d pydk0.e+lm:z. 9jdzvoto +3o0ecn+hqafns produced when an electron and a positron, each with 420 keV of kinetic energy, annihilate head foqna3 e+0 +chon? $\lambda $ $\approx $ $ \times 10^{-12}\ \text{m}$
