Question

Physics : Please answer fast

Answer 1

$\int\limits^2_b {\frac{1}{r^2} } \, dx \\\\-1\int\limits^2_1 {\frac{1}{r} } \, dr\\ \\-1[\frac{1}{2} - 1 ]\\\\-1 [ -\frac{1}{2}]\\\\\frac{1}{2}$