Using the transformation x + y = u, y = v. The value of Jacobian (J) f...
To solve this problem, we need to evaluate the integral:
∫01 ∫01 |cos(x + y)| dx dy
using the transformation x + y = u and y = v.
Step 1: Determine the Transformation and Jacobian
The transformation is given by:
To express x and y in terms of u and v:
- From u = x + y, we can solve for x as x = u - v.
- Thus, x = u - v and y = v.
Now, we need to calculate the Jacobian J of the transformation:
Calculating each partial derivative:
- ∂x/∂u = 1
- ∂x/∂v = -1
- ∂y/∂u = 0
- ∂y/∂v = 1
So, the Jacobian is:
J = | 1 -1 | = (1)(1) - (-1)(0) = 1.
| 0 1 |
Thus, the Jacobian J = 1.
Step 2: Set Up the Integral in Terms of u and v
Since J = 1, the integral becomes:
∫01 ∫01 |cos(u)| du dv.
Step 3: Evaluate the Integral
We can separate the integrals because |cos(u)| depends only on u:
∫01 ∫01 |cos(u)| du dv = ∫01 ( ∫01 |cos(u)| du ) dv.
First, we evaluate the inner integral with respect to u:
∫01 |cos(u)| du.
Since cos(u) is positive over the interval [0, 1], we have:
∫01 cos(u) du = [sin(u)]01 = sin(1) - sin(0) = sin(1).
Now, substitute this result back:
∫01 ∫01 |cos(u)| du dv = ∫01 sin(1) dv = sin(1) * [v]01 = sin(1).
Conclusion:
The value of the integral is approximately: B: 1.