Graph the ellipse and locate the foci x^2/36+y^2/11=1.
I got tthe following:
1/36 x^2 + (0)^2/11=1
1/35x^2=1
x^2=1x36
x=+- squar root of 36
x= +6, -6
-------------------
0/36+1/11y^2=1
y^2=11
y= +square root of 11, - square root 11
---------------------------
answer is foci at (square root 11, 0) and (negatie square root 11,0)

Question

Graph the ellipse and locate the foci x^2/36+y^2/11=1. 
I got tthe following:  
1/36 x^2 + (0)^2/11=1
1/35x^2=1
x^2=1x36
x=+- squar root of 36
x= +6, -6
-------------------
0/36+1/11y^2=1
y^2=11
y= +square root of 11, - square root 11
---------------------------
answer is foci at (square root 11, 0) and (negatie square root 11,0)

anonymous · Answer

no

anonymous · Answer

Okay, what went wrong?

anonymous · Answer

your foci are wrong

anonymous · Answer

do you know how this is oriented?

anonymous · Answer

|dw:1410490350847:dw|

anonymous · Answer

Well, I know because the denominator of x^2 is grater than y^2, the major axis is horizontal. The other possible horizontal answer would be focie at (5,0) and (-5,0).

anonymous · Answer

But where did I go wrong when I got the other answer?

anonymous · Answer

let me ask again
you need to know which way the ellipse is oriented to get the right answer

anonymous · Answer

The ellipse would be horizontal.
.

anonymous · Answer

oh  i see you answered, the major axis is horizontal

anonymous · Answer

Thanks.

anonymous · Answer

and the center is $(0,0)$ so the foci are to the left and right of the center

anonymous · Answer

That's is correct.

anonymous · Answer

you have $a^2=36,b^2=11$ you need $a^2-b^2$

anonymous · Answer

Hold on.  I am doing this.

anonymous · Answer

1296-121=1175

anonymous · Answer

ooh no 
don't square them !  they are already squared

anonymous · Answer

$$a^2=36,b^2=11,a^2-b^2=36-11=25$$

anonymous · Answer

Sorry, my bad..  I see a square and I square it.

anonymous · Answer

right, don't do tha?
that makes $c^2=25$ and so $c=5$ making your foci 5 units to the left and right of the center

anonymous · Answer

So then that would make a 5 and a -5.

anonymous · Answer

Answer would be foci at (5,0) and (-5,0).

anonymous · Answer

I have been at this most of the day and have accomplished 8 questions.  The book is not really explicit in explanations, so am trying my best.  I am only on to see if I got it right or where I went wrong.   Thank you for explanations.  That makes everything much easier.

anonymous · Answer

Thanks everyone for your help tonight.  Two questions out of eight were uncertain and they are now answered.  Thank you so much for everyone's help.  Will be back for sure.

anonymous · Answer

oh sorry i  stepped away
yes $(-5,0)$ and $(5,0)$

anonymous · Answer

if you want to see nice easy worked out examples, google "ellipse purplemath" and they have many easy to follow