Matrices & Systems of Equations:Matrix Algebra

Hello could someone please help me with the following problems, I just couldn't find my way around it. Thanks!

1) Given the following:

A equals

1 2

1 -2

**b **equals

4

0

**c **equals

-3

-2

write c as a linear combination of column vectors a_1 & a_2

2) Let A equals

a_11 a_12

a_21 a_22

Show that if d = a_11 a_22 - a_21 a_12 is not equal 0, then

A inverse equals

1/d * ( {a_22 -a_12} {-a_21 a_11} ) ====> {row 1} {row 2}

Matrices and Systems Equations

I still don't get number two. :confused:Once multiplying the matrices, then where do I go from there? And what is the 2*2 identity matrice?