About a type of equations

Question

In physics, there appear a type of equations following this format,

$ Q2 = Q1(1 + a \Delta T) $

Where Q1 is the first quantity

Q2 is the changed quantity,

a is the changing coefficient,

$ \Delta T $ is the change of the factor (for example, temperature)

They appear in equations on resistance, expansion etc.

Deriving them are simple, But what I like to know is what this type of relations are called in general.

Thanks.

Edit: with T I meant a change, so i've added a Delta for it as pointed out in the comments.

Answer 1

Let $q2=y,dT=x $(for small interval) since $q1,a $ are constant then equation is $y=q1+mx $ where $m=q1a $ thus the equation is a linear approximation for a function when $x $ is very very small.