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10. The following three point charges are placed on the x axis: +5.0 mC at x=0; +4.0 mC at x= 40 cm; and +6.0 mC at x= +80 cm. Find (a) the electric field magnitude and direction and (b) the electric potential at x= +10 cm.
a) E = k(5E6)/.102 +k(4E6)/.502  k(6E6)/.702 = +4.5E6 N/C (in +x direction)
I was just wondering, how did the teacher get .102, .502 and .702 as the radius's.

physics 
drwls
x is 0.70 m from the 6 mC charge, 0.50 m from the 4 mC charge, and 0.10 m from the 5 mC charge
I also do not understand why the number "0.002" was added to those distances (in meters). It appears to be a misprint.
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