coulomb's law problem question?

M

MayraM

New member
3 charged particles are located at the corners of an equilateral triangle
calculate the total force

y--------------O + 7.00 uC




-------O---------------O-----> X
+2.00 uC -4.00 uC
F1= Ke q1q2/r^2 = 0.503N
F2= 1.01N

Fx= F1cos60.0 + F2cos60.0 = 0.755N
Fy= F1sin60.0 - F2sin60.0 = -0.436N

My question is here:

F = (0.755N)i - (0.436N)j = 0.872N at an angle of 330 degreeds

how they arrive to 0.872N (I tried subtraction not get the same answer)?
 
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