Problem: -x^2 + 4x(adsbygoogle = window.adsbygoogle || []).push({});

- ( x^2 - 4x + (4/2)^2 ) - 4

= - (x - 2) - 4

Vertex is at (2, -4)

but the vertex is obviously at (2,4)...

what did I do wrong.

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# Completing the square

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