# What am I doing wrongly?

• Nov 12th 2011, 08:35 AM
benny92000
What am I doing wrongly?
I have the following equation:

36x^(4)-126^(2)+108=0

The solutions are -1.41, 1.41, -1.22, 1.22 I was attempting to expedite the process of plugging in these numbers to said equation, so I put the above equation in y1 exactly as I typed it (except, of course, without the = 0.) Then I went to the homescreen and hit vars-yvars-function-y1 then i put (1.22, etc.) to test the points. None of them equalled zero... I am using TI 83 plus. Thanks for the help.
• Nov 12th 2011, 10:27 AM
skeeter
Re: What am I doing wrongly?
Quote:

Originally Posted by benny92000
I have the following equation:

36x^(4)-126^(2)+108=0

The solutions are -1.41, 1.41, -1.22, 1.22 I was attempting to expedite the process of plugging in these numbers to said equation, so I put the above equation in y1 exactly as I typed it (except, of course, without the = 0.) Then I went to the homescreen and hit vars-yvars-function-y1 then i put (1.22, etc.) to test the points. None of them equalled zero... I am using TI 83 plus. Thanks for the help.

I assume you mean ...

$y = 36x^4 - 126x^2 + 108$

$18(2x^2 - 3)(x^2 - 2) = 0$

$x = \pm \sqrt{2}$

$x = \pm \sqrt{\frac{3}{2}}$

if you're using those rounded solutions in Y1, the calculator will not give you back 0. my advice is store the unrounded solutions into a alpha register and try evaluating the stored value.
• Nov 12th 2011, 11:21 AM
benny92000
Re: What am I doing wrongly?
Great, thanks!