Question

Approximate to the nearest tenth the real zeros of f(x) = –5x3 + 9x2 + 12x + 2.

answers:
The zeros are approximately 0.2, 0.7, and 2.7.
The zeros are approximately –2.7, –1.7, and 0.2.
The zeros are approximately –0.2, –0.7, and 2.7.
The zeros are approximately –0.5, –0.7, and 1.7.

Answer 1

try sum of roots thing i guess..

Answer 2

\[-5 x^3 + 9 x^2 +12 x+ 2=(-5 x-1) \left(x^2-2 x-2\right) \]

Answer 3

what is that @ robtobey thats not the one of th answers

Answer 4

or is it?

Answer 5

\[\left\{-\frac{1}{5},1-\sqrt{3},1+\sqrt{3}\right\}\to \{-0.2,-0.732051,2.73205\} \]Sorry, There was a sign mistake for the 1/5

Answer 6

robtobey may you please explain how you guess roots ? (i heard of a method of some divisors of one of the numbers in the expression ?)

Answer 7

i mean roots for the factorization

Answer 8

Used Mathematica's Factor function.
Refer to the attachment. Mathematica leaves the terms in reverse order, still valid though.

Answer 9

this is a cubic so in theory it can be solved exactly.
why dont you use your graphing calculator,

Answer 10

dont know how to plug it in dude

Answer 11

here you knucklehead http://www.wolframalpha.com/input/?i=solve++%E2%80%935x3+%2B+9x2+%2B+12x+%2B+2%3D0

Answer 12

thanks dude

Answer 13

:)

Answer 14

For the general non factorable cubic Mathematica provides the NSolve function.
Refer to the attachment.

Answer 15

ok so you didnt do it by hand

Answer 16

No. I am not a student in school.

http://www.ted.com/talks/conrad_wolfram_teaching_kids_real_math_with_computers.html