Four negatively charged particles each carry a charge qn and form a square of side length d. A positively charged particle carrying a charge qp is at the square's center.
If the arrangement is in equilibrium (the vector sum of the electric forces on each particle is zero), what is the numerical value of the ratio qp/qn?

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y