9 come form the scaling in x-axes and y-axes and also the y!that what I want to understand

Err, well, the factor comes from the separate scalings and the fact that an area is two-dimenional: The area is the product of the two lengths (assuming they are orthogonally oriented, like principal x and y axes are), so when the original area is

A := x * y

and the lengths are scaled by 3/4, the resulting area is

A' := ( 3/4 * x ) * ( 3/4 * y ) = ( 3/4 * 3/4 ) * ( x * y ) = 9/16 * A

9 come form the scaling in x-axes and y-axes and also the y!that what I want to understand

Err, well, the factor comes from the separate scalings and the fact that an area is two-dimenional: The area is the product of the two lengths (assuming they are orthogonally oriented, like principal x and y axes are), so when the original area is

A := x * y

and the lengths are scaled by 3/4, the resulting area is

A' := ( 3/4 * x ) * ( 3/4 * y ) = ( 3/4 * 3/4 ) * ( x * y ) = 9/16 * A

Ok!

Thank you alot