[tex]b= \frac{ \sqrt{(13+5)(13-5)} }{ \sqrt{(10+8)(10-8)} } = \frac{ \sqrt{18*8} }{ \sqrt{18*2} } = \frac{ \sqrt{18}* \sqrt{8} }{ \sqrt{18}* \sqrt{2} }= \frac{ \sqrt{8} }{ \sqrt{2} }= \frac{ \sqrt{2*4} }{ \sqrt{2} }= \frac{ \sqrt{2}* \sqrt{4} }{ \sqrt{2} }= \sqrt{4}=2 [/tex]