more hyperbolic function questions

Hi

I need help on the following:

1)Given $\displaystyle sinh(u) = 2 and sinh(u) = 7 evaluate sinh(u-v)$

I used $\displaystyle sinh(u-v) = sinh(u)cosh(v) - cosh(u)sinh(v)$ but still was not unable to get the final values.

2) Given the parmaetric equations x=2cos(t), y=3sin(t) use the identity $\displaystyle cos^2(t) + sin^2(t) = 1$

This is what i have done:

$\displaystyle

2x^2 + 3y^2 = 1$

Can someone tell me why this is incorrect and this is correct:

$\displaystyle \frac{x^2}{4}+\frac{y^2}{9} = 1$

P.S