In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
y = 3 x² + 5
vertex = ?
Step 02:
y = ax² + bx + c
xv = - b / 2a
y = 3 x² + 5
a = 3 , b = 0 , c = 5
If xv = 0
yv = 3 * (0)² + 5
yv = 5
The answer is:
Vertex ( 0 , 5)