Answer
$d \approx 12.38$
Work Step by Step
$$\eqalign{
& {\text{Let the points: }}\underbrace {\left( {4,2.5} \right)}_{\left( {{r_1},{\theta _1}} \right)}{\text{ and }}\underbrace {\left( {12,1} \right)}_{\left( {{r_2},{\theta _2}} \right)} \cr
& {\text{Apply }}d = \sqrt {r_1^2 + r_2^2 - 2{r_1}{r_2}\cos \left( {{\theta _1} - {\theta _2}} \right)} \cr
& d = \sqrt {{{\left( 4 \right)}^2} + {{\left( {12} \right)}^2} - 2\left( 4 \right)\left( {12} \right)\cos \left( {2.5 - 1} \right)} \cr
& {\text{Simplifying}} \cr
& d = \sqrt {16 + 144 - 96\cos \left( {2.5 - 1} \right)} \cr
& d \approx \sqrt {160 - 6.7907} \cr
& d \approx 12.38 \cr} $$