If f(x) = x2 - 3x + 1 and f(2 a) = 2f(a) then a is equal to​

For these question, it has two separate equations: 2f(a) and f(2a) .

For f(2a) equations its x=2a, so you must substitute 2a into the f(x) equation

For 2f(a), it means the two time of f(a) equation with x=a, so you substitute a inti f(x) equation first, then you multiply it by 2.

heat the gas and measure the pressure

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement