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**[SOLVED] Quick Question.....I have the answer with steps, but can't figure out how th**

## Homework Statement

Two charges of 1.5x10^6C and 3x10^-6C are .20m apart. Where is the electric field between them equal to zero?

## Homework Equations

## The Attempt at a Solution

Variables

Variables

r(total)= .2m

q1= 1.5x10^-6

q2=3x10^-6

(r2)^2= (.20 - r1)^2

E1 = E2

kq1/(r1)^2 = kq2/(r2)^2

1.5x10^-6C/(r2)^2 = 3.0x10^-6C/(r2)^2

since

(r2)^2 = 2(r1)^2

substitude for (r2)^2 and rearrange:

0= (r1)^2 + .4r1 - 4.0x10^-2

kq1/(r1)^2 = kq2/(r2)^2

1.5x10^-6C/(r2)^2 = 3.0x10^-6C/(r2)^2

since

(r2)^2 = 2(r1)^2

substitude for (r2)^2 and rearrange:

0= (r1)^2 + .4r1 - 4.0x10^-2

then quadratic forumula......

the part I highlighted where it turns from red to blue, is the step I don't understand. I tried to rearrange it, but it doesn't come out as a quadratic as the book answer does.

the part I highlighted where it turns from red to blue, is the step I don't understand. I tried to rearrange it, but it doesn't come out as a quadratic as the book answer does.