how do u evaluate determinants ?

Answer 1

ex:
if u have:
| x y |
| u v | = x*v - u*y
it means u do a cross product between the elements but the signs of the product is as follows
| + - |
| - + |

ex:
if u have:
| x y z |
| i j k | = x * (j*w - vk) - y * (i*w - u*k) + z * (i*v - j*u)
| u v w |

Answer 2

Probably the best way is to use elementary
row operations to reduce the determinant
to triangular form. I.E., one with zeros below
the main diagonal. Then just multiply
the resulting diagonal elements to get
the answer.