The formula for radiant strike level 10 is
For lvl 10 radiant we have M=37
And for Keberos we have
And tolerance= 0.57
This is the keberos labelled 1, and it has the lowest tolerance.
Putting these numbers in the formula you get:
Which gives a damage of 7803
Basically you will need to master radiant to KO with the amount stated in the thread.
If you require the know the MA for another level of the skill, solve this equation. For MA.
To do so, go to wolframalpha.com and replace M with the magnification; and MA with x and type "9050=0.57*((x-49)*37-1628) solve for x" into the box.
You will get x=522
Replace 37 with 46 for mastery and you get x=430; this is one MA off what the thread requires.