# Need help in finding all complex solutions

• Nov 23rd 2013, 04:33 PM
asilvester635
Need help in finding all complex solutions
I tried working it out but I didn't get the right answer... Btw the correct answer is "B" which is highlighted.... What did I do wrong?
• Nov 23rd 2013, 04:44 PM
topsquark
Re: Need help in finding all complex solutions
Quote:

Originally Posted by asilvester635
I tried working it out but I didn't get the right answer... Btw the correct answer is "B" which is highlighted.... What did I do wrong?

You have the right idea, but you factored wrong. \$\displaystyle (x^2)^2 - 8(x^2) - (3^2) \neq ( (x^2) - 3 )^2\$. How do you factor \$\displaystyle y^2 - 8y - 9\$?

-Dan
• Nov 23rd 2013, 05:01 PM
Plato
Re: Need help in finding all complex solutions
\$\displaystyle x^4-8x^2-9=(x^2-9)(x^2+1)\$.
• Nov 23rd 2013, 05:11 PM
Prove It
Re: Need help in finding all complex solutions
Quote:

Originally Posted by Plato
\$\displaystyle x^4-8x^2-9=(x^2-9)(x^2+1)\$.

Which factorises further :P
• Nov 23rd 2013, 05:15 PM
Plato
Re: Need help in finding all complex solutions
Quote:

Originally Posted by Prove It
Which factorises further :P

But why do that? The roots are perfectly obvious from that product.
• Nov 23rd 2013, 05:18 PM
Prove It
Re: Need help in finding all complex solutions
Quote:

Originally Posted by Plato
But why do that? The roots are perfectly obvious from that product.

To you and me perhaps, not to everyone though...