Explanation:
minimum.
since the term with x² has a positive factor, this will grow exponentially in the positive direction compared to the other terms, so y (the functional value) will grow and grow with growing distance of x to the vertex.
and that makes the vertex the minimum of the parabola (which opens upwards).
if the factor would be negative (like -x² - 2x + 10), the vertex would be a maximum, and the parabola would open downwards.