Suppose … is the wedge … moved up so that the sharp…

R is a pie-shaped wedge: $0⩽r⩽1$ and $\pi /4⩽\theta ⩽3\pi /4$.

Suppose $R^{\ast }$ is the wedge $R$ moved up so that the sharp point is at $x=0$, $y=1$.
(a) Find limits on $\iint dydx$ to integrate over $R^{\ast }$.
(b) With $x^{\ast }=x$ and $y^{\ast }=y-1$, the $xy$ region $R^{\ast }$ corresponds to what region in the $x^{\ast }{y}^{\ast }$ plane?
(c) After that change $dxdy$ equals \_\_\_\_\_\_ $d{x}^{\ast }d{y}^{\ast }$.

Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §14.2 Change to Better Coordinates, #7