R5 equals R4 || R6 (resistors in parallel) calculated as $$R5 = \frac{R4 * R6}{R4 + R6}$$ and its purpose is to balance the two inputs of the opamp, it cancels the differences caused by the opamp input bias current

http://www.ecircuitcenter.com/Circuits/op_ibias/op_ibias.htm

R5 equals R4 || R6 (resistors in parallel) calculated as $$R_5 = \frac{R_4 \cdot R_6}{R_4 + R_6}$$ and its purpose is to balance the two inputs of the opamp, it cancels the differences caused by the opamp input bias current

http://www.ecircuitcenter.com/Circuits/op_ibias/op_ibias.htm

R5 equals R4 || R6 calculated as ((R4*R6)/(R4+R6)) and its purpose is to balance the two inputs of the opamp, it cancels the differences caused by the opamp input bias current

http://www.ecircuitcenter.com/Circuits/op_ibias/op_ibias.htm

R5 equals R4 || R6 (resistors in parallel) calculated as $$R5 = \frac{R4 * R6}{R4 + R6}$$ and its purpose is to balance the two inputs of the opamp, it cancels the differences caused by the opamp input bias current

http://www.ecircuitcenter.com/Circuits/op_ibias/op_ibias.htm