Please include an explanation as well. Thank You!

[tex]A = \frac{B r_{1}r_{2}}{ C {x}^{2} } \\ = > A C {x}^{2} = B r_{1}r_{2} \\ = > r_{1} r_{2} = \frac{A C {x} ^{2} }{B} \\ = > r_{1} = \frac{A C {x} ^{2} }{B r_{2}} [/tex]
[tex]r_{1} = \frac{A C {x} ^{2} }{B r_{2}} [/tex]
Hope it helps.
Do comment if you have any query.