Three charges each of magnitude 3 nC are at separate corners

Three charges, each of magnitude 3 nC, are at separate corners of a square of edge length 2 cm. The two charges at opposite corners are positive, and the other charge is negative. Find the force exerted by these charges on a fourth charge q = +3 nC at the remaining (upper right) corner. (Assume the +x axis is directed to the right and the +y axis is directed upward.)

Solution

               /\\F34
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Q1--------------Q4===> F14
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Q2--------------Q3

Q1 = Q3 = 3nC
Q2 = -3nC
q4 = 3nC

k = 8.99*10^9 N m2/C2

F14 = kq^2/R^2 = 8.99*10^9*(3*10^-9)^2/(0.02)^2 = 0.000202275 = 2.0227*10^-4

F34 = kq^2/R^2 = 8.99*10^9*(3*10^-9)^2/(0.02)^2 = 0.000202275 = 2.0227*10^-4

F24 = -kq^2/R^2 = -8.99*10^9*(3*10^-9)^2/(0.0283)^2 = -0.000101025 = -1.01025*10^-4

Fnet = (2.0227*10^-4 - 1.01025*10^-4cos45)i + (2.0227*10^-4 -1.01025*10^-4sin45) j
Fnet = 0.000130835 i + 0.000130835 j
Fnet = 0.000185025 = 1.85*10^-4