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+1
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Hi good people!,

 

kindly just check if I did this correctly?

 

Make r the subject:

 

\(F=K{Q1Q2 \over r^2}\)

 

I did this:

 

devide by K:

 

\({F \over K}={Q1Q2 \over \ r^2}\)

 

Multiply by r^2

 

\({Fr^2 \over K}=Q1Q2\)

 

Multiply by K

 

\(Fr^2=K(Q1Q2)\)

 

Devide by F

 

\(r^2={K(Q1Q2) \over F}\)

 

\(r= \sqrt{K({Q1Q2} \over F}\)

 

Thanx for the time!

Guest Feb 21, 2018

Best Answer 

 #1
avatar+7266 
+3

Your method is correct, but you can do it without dividing by K and then multiplying by K :

 

\(F\,=\,K\cdot\frac{Q_1Q_2}{r^2} \\~\\ F\,=\,\frac{K(Q_1Q_2)}{r^2}\)

                                  Multiply both sides of the equation by  r2

\(Fr^2\,=\,K(Q_1Q_2)\)

                                  Divide both sides of the equation by  F .

\(r^2\,=\,\frac{K(Q_1Q_2)}{F} \)

 

If we need to include both solutions for  r  ,  then we need to take the positive and negative square root of both sides.

 

\(r\,=\,\pm\sqrt{\frac{K(Q_1Q_2)}{F}}\)

hectictar  Feb 21, 2018
 #1
avatar+7266 
+3
Best Answer

Your method is correct, but you can do it without dividing by K and then multiplying by K :

 

\(F\,=\,K\cdot\frac{Q_1Q_2}{r^2} \\~\\ F\,=\,\frac{K(Q_1Q_2)}{r^2}\)

                                  Multiply both sides of the equation by  r2

\(Fr^2\,=\,K(Q_1Q_2)\)

                                  Divide both sides of the equation by  F .

\(r^2\,=\,\frac{K(Q_1Q_2)}{F} \)

 

If we need to include both solutions for  r  ,  then we need to take the positive and negative square root of both sides.

 

\(r\,=\,\pm\sqrt{\frac{K(Q_1Q_2)}{F}}\)

hectictar  Feb 21, 2018
 #2
avatar
+1

Sweet,

 

thanx a million Hectictar!!

Guest Feb 21, 2018

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