Posted by Zach on Sunday, November 15, 2009 at 9:30pm.
Write a quartic function that has roots that are 3+5i, -4 and 7 and
I have tried it a bunch of times and can't seem to get it.
I multiplied them together
I was a little unsure what f(-3)=53 means.
I thought I should plug -3 in for x and it should equal 53. That doesn't work.
Can you please help me see where I went wrong?
- Pre Calc - Reiny, Sunday, November 15, 2009 at 10:12pm
Ahh, how would you know that the function wasn't
f(x) = a(x-3+5i)(x-3-5i)(x+4)(x-7)
Wouldn't it still have those same roots if you set f(x) = 0 ?
I am going to trust that you expanded correctly.
Now let f(-3) = 53
53 = a((-3)^4 - 9(-3)^3 + 24(-3)^2 + 66(-3) - 952)
solve for a, then multiply your expanded expression by that value.
- Pre Calc (please explain) - Bob Dylan, Sunday, November 15, 2009 at 10:23pm
How do you know that it is supposed to have an a in front?
- Pre Calc - Zach, Sunday, November 15, 2009 at 10:47pm
I get where a comes from. Is the answer 53/-610? It doesn't seem right.
- Zack Pre Calc - Reiny, Sunday, November 15, 2009 at 10:56pm
I got -53/610 also
- Bob Dylan - Pre Calc - Reiny, Sunday, November 15, 2009 at 10:59pm
" How do you know that it is supposed to have an a in front? "
Bob, I guess the answer was blowing in the wind.
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