Which of the following equations is used to find the value of c?

a²+b²=c²
c²+b²=a²
a²+c²=b²
a²+b²+c²=1

Question

Which of the following equations is used to find the value of c?

a²+b²=c²
c²+b²=a²
a²+c²=b²
a²+b²+c²=1

tkhunny · Answer

For what?  It's different for ellipses and hyperbolas.

anonymous · Answer

ellipses sorry

tkhunny · Answer

Go look back at the last problem.  The answer is in there.  You must remember from one problem to the next!  :-)

anonymous · Answer

@tkhunny you said b2=a2−c2 but that is not an option here

tkhunny · Answer

You must also remember your algebra.

Here's what I said: b^2 = a^2 - c^2
That is the same as this: b^2 + c^2 = a^2
That is the same as this b^2 - a^2 = -c^2
That is the same as this: -a^2 = -b^2 - c^2
That is the same as this: c^2 = a^2 - b^2

Are you seeing it, yet?

anonymous · Answer

oh okay so it is the same?

anonymous · Answer

a^2+c^2=b^2 is the answer in that case? @tkhunny

tkhunny · Answer

No, you jut changed one sign.  That's no good.

This we have established: b^2 = a^2 - c^2

Notice how all four chhoices are absent any negative signs.  Rewrite the known expression, making sure there is nothgin engative when you are done.

b^2 = a^2 - c^2 is hte same as b^2 + c^2 = a^2  Do we have that one?

anonymous · Answer

ohhh okay i see now, yes that is an option thank you so much. i have just one or two more problems i need help with.. i'll repost now can you please help? @tkhunny