# Parametric equations - againWatch

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#1
I'm getting totally confused over this:

Take the following example:

Find suitable parametric equations for:

y^2 - 4x^2 = 1

---

I got the result which is not a problem:

x= 1/2 tanA, y = secA

But...

What if I had been presented with the exercise the other way round?

How could I get from

x= 1/2 tanA, y = secA

to

y^2 - 4x^2 = 1

Help...

jorge
0
14 years ago
#2
(Original post by Jorge)
I'm getting totally confused over this:

Take the following example:

Find suitable parametric equations for:

y^2 - 4x^2 = 1

---

I got the result which is not a problem:

x= 1/2 tanA, y = secA

But...

What if I had been presented with the exercise the other way round?

How could I get from

x= 1/2 tanA, y = secA

to

y^2 - 4x^2 = 1

Help...

jorge
2x = tana
4x^2 = tansqa (1)

y^2 = secsqa = 1 + tansqa
y^2 -1 = tansqa (2)

(1) and (2) => 4x^2 = y^2 -1
y^2 -4x^2 =1

Aitch
0
#3
(Original post by Aitch)
2x = tana
4x^2 = tansqa (1)

y^2 = secsqa = 1 + tansqa
y^2 -1 = tansqa (2)

(1) and (2) => 4x^2 = y^2 -1
y^2 -4x^2 =1

Aitch

Brilliant! Thanks. Got it!

Jorge
0
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