Question Number 154210 by Eric002 last updated on 15/Sep/21
Commented by Eric002 last updated on 15/Sep/21
$${the}\:{indentical}\:{circles}\:{of}\:{radius}\:{r},\:{inside} \\ $$$${a}\:{triangle},\:{each}\:{of}\:{them}\:{tangent}\:{to}\:{tow}\: \\ $$$${sides}\:{of}\:{the}\:{triangle}. \\ $$$${prove}:\frac{\mathrm{1}}{{r}}=\frac{\mathrm{1}}{{R}_{{in}} }+\frac{\mathrm{1}}{{R}_{{out}} } \\ $$$${R}_{{in}} ={inradius}\:{of}\:\Delta{ABC} \\ $$$${R}_{{out}} ={circumradius}\:{of}\:\Delta{ABC} \\ $$
Commented by mr W last updated on 18/Sep/21
$${see}\:{Q}\mathrm{154415} \\ $$