For the transformation

the Jacobian is

with determinant

The vertices of the triangle in the
-plane are



Then the integral is

It's difficult to make out, but I think the task is to expand

Write the number in polar form first:

By DeMoivre's theorem, you have

and converting back to Cartesian form, this number is equivalent to
Answer:
the equation is equivalent, y is any number
Step-by-step explanation:
-3(3y-7) = 21-9y
-9y + 21 = 21 - 9y
-9y = -9y
y=y
any number will satisfy y=y
We let f(0) = 235
After 1 month,
f(1) = 235*(0.7) + 50
After 2 months,
f(2) = 235*0.7*0.7+ 50*2
And so on..
Therefore, we can represent the number of MP3 players in the store after n months with the function:
f(n) = 235 (0.7)^n + 50n