My teacher wrote the following:

**Constant Acceleration**

If acceleration is constant, then:

$$\vec{v}(t) = \int\_0^t \vec{a}(t')dt'\ + \vec{v\_0}$$

and

$$\vec{x}(t) = \int\_0^t \vec{v}(t')dt'\ + \vec{x\_0}$$

Why does acceleration need to be constant? I can't see why integration would need a constant acceleration as such.