Posted by **Zoey** on Wednesday, May 2, 2012 at 10:17pm.

for the conic y=5x^2-40x+78 find an equation in standard form and its vertex, focus, and directrix

- Pre-Calc -
**Reiny**, Wednesday, May 2, 2012 at 10:24pm
complete the square

y = 5(x^2 - 8x + ....) + 78

= 5(x^2 - 8x + 16 - 16) + 78

= 5( (x-4)^2 - 16) + 78

= 5(x-4)^2 - 80 + 78

= 5(x-4)^2 - 2

take over ....

- Pre-Calc -
**Zoey**, Wednesday, May 2, 2012 at 10:48pm
What's my next step??

- Pre-Calc -
**Reiny**, Wednesday, May 2, 2012 at 11:10pm
We could write our answer in the form

y+2 = 5(x-4)^2

take a look at

http://jwilson.coe.uga.edu/emt725/class/sarfaty/emt669/instructionalunit/parabolas/parabolas.html

half-way down the page at example 3

and follow the steps.

- Pre-Calc -
**Zoey**, Wednesday, May 2, 2012 at 11:11pm
thank you!

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