Maximum number of turning points? Algebra

Question

What is the maximum number of turning points in the graph of P(x) = 2x² + 14x - 7?
Question options:

a) 1

b) 2

c) 3

d) 4

 

Please explain this

Answer 1

a) 1 is the answer

2x^2 +14x-7 is an upward opening parabola

= 2(x^2 +7x) -7 -49/2

= 2(x+3.5)^2 - 31.5

it goes down until x=-3.5, then it goes up

just one turning point at (-3.5, -31.5) = vertex = minimum point