For any electromagnetic wave, the relationship between frequency and wavelength is given by
[tex]\lambda = \frac{c}{f} [/tex]
where
[tex]\lambda[/tex] is the wavelength
c is the speed of light (the speed of the electromagnetic wave)
f is the frequency
For the X-rays in our problem, the frequency is [tex]f=1.0 \cdot 10^{19}Hz[/tex], while the speed of light is [tex]c=3.0 \cdot 10^8 m/s[/tex], so the wavelength of this radiation is
[tex]\lambda= \frac{3 \cdot 10^8 m/s}{1.0 \cdot 10^{19} Hz} =3 \cdot 10^{-11} m[/tex]
