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A temperature variation can be calculated in Kelvin or in degrees Celsius. To convince yourself of this, let's take for example two temperatures \(T_1\) and \(T_2\) given in ° C. To convert them to Kelvin, we must add 273.15. The temperature variation \( \triangle T\) therefore gives:
$$\triangle T = T_1-T_2$$ 
$$\triangle T = (T_1+273,15)-(T_2+273,15)$$
By distributing the negative sign in the second part of the equation, we obtain:
$$\triangle T = T_1\color{red} {+273,15} \color{black} {-T_2} \color{red} {-273,15}$$
We therefore notice that the 273.15 cancel each other out, which amounts to our starting equation.
When the formula includes  \( \triangle T\) , you can use either temperatures in Kelvin or in degrees Celsius since we have just shown that:
$$\triangle T = T_1-T_2 = (T_1+273,15)-(T_2+273,15)$$
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