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# Manipulate

+1
232
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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!

Feb 21, 2018

#1
+7354
+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.

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

.
Feb 21, 2018

#1
+7354
+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
#2
+1

Sweet,

thanx a million Hectictar!!

Guest Feb 21, 2018