This question seems to me to be an exercise in applying the rule for a difference of squares in order to rewrite the difference of two relatively large numbers as the "simpler" product of other integers.
The space diagonal will have length ...
... d = √(1² +4² +2²) = √(1 +16 +4) = √21
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This can be found using the Pythagorean theorem. A drawing can help. Find the length of any face diagonal, then use that length as the leg of a right triangle whose hypotenuse is the space diagonal and whose other leg is the edge length not used in the first calculation.
Answer: radius=3
X = -2
Y = 5
Step-by-step explanation:
Vjghhghfhghghvhhfhfhchdhdhhd
C=10 and D=7 because 10+7=17 and 10-7=3