Vertex of a parabola

[lhwalker]

I am helping with curriculum at my school and noticed EngageNY Algebra I, Module 4, Lesson 8, Graph Vocabulary defines the axis of symmetry as “the vertical line given by the graph of the equation x = -b/(2a).” Memorizing and using that formula does not seem to be required for the unit and it is not in the Standards, so am I correct to assume that formula does not need to even be presented to the students because they can complete the square and derive the equation of the line of symmetry from that form? I’m thinking that formula is part of the mile-wide problem we are trying to address by adopting the CCSS.

[Bill McCallum]

I completely agree, Lane.

[Anonymous]

Lane, were thinking of students doing something like this to find the line of symmetry?
(x – a)^2 + k is the quadratic with the square completed.
Then they solve
(x – p – a)^2 + k = (x + p – a)^2 + k for x?

[lhwalker]

I would write (x-h)^2 + k Using h and k is pretty much textbook standard for shifts on conics (although students need to know variables are variables). Since h is the horizontal shift from the origin, the line of symmetry runs through x=h

[Author]

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