What do you do to check whether a number is rational or irrational

In the field of thermodynamics, rankine is the unit used to measure temperature. one can convert temperature from celsius into rankine using the formula c= r/1.8 - 273, what is the temperature in celcius corresponding to r degrees rankine.

What is the value of r of the geometric series?

Me complete this proof! prove that a quadrilateral is a square. me with the steps for this proof.