Make a change of coordinates:
The Jacobian for this transformation is
and has a determinant of
Note that we need to use the Jacobian in the other direction; that is, we've computed
but we need the Jacobian determinant for the reverse transformation (from
to
. To do this, notice that
we need to take the reciprocal of the Jacobian above.
The integral then changes to
Length x width is the formula.
so 18 x 18 for 7.
22 x 24 for 8.
and 8 would probably be 5 x 5 to equal 20. so the length and width would be 5 and 5 because 20 is the area
The answer is -2.
im sorry if the work is messy.