# Math Help - Making r the subject

1. ## Making r the subject

Hey guys,

As Im a noob at maths I need your help in making r the subject so I can figure out the radius of my nanoparticles. Can someone please help

2. Hi Donut

Mulitply both sides through by $r^2$

you can then use the quadratic formula to solve for r.

3. hmm thats what I thought I should do but I get keep getting this obscenely small number. Back to the drawing board I guess >_<