In a triangle $A B C$, if $\left(r_1-r_3\right)\left(r_1-r_2\right)-2 r_2 r_3=0$, then $a^2-b^2=$

• A

  $c^2+\frac{b^2}{4}$
• Correct answer
  B

  $c^2$
• C

  abc
• D

  $\frac{b+a}{c}$

Hence, the correct answer is option: 'B'.