Question 879488
To find the inverse of a 2x2 matrix. 
{{{A=(matrix(2,2,a,b,c,d))}}}
Then,
{{{A^(-1)=(1/(ad-bc))*(matrix(2,2,d,-b,-c,a))}}}
So,
{{{1/(ad-bc)=1/(7(3)-(-4)(-5))=1/(21-20)=1}}}
{{{A^(-1)=(matrix(2,2,3,4,5,7))}}}