integ(x*cos(x), x, [0,1])
Let's compute the integral: ∫(x·cos(x))dx
For x·cos(x), we use integration by parts: ∫(u1·v2')dx = u1·v2 + ∫(u1'·v2)dx, with u1 = x and v2' = cos(x)
Thus, u1' is 1
Let's compute the integral v2': ∫(cos(x))dx
sin(x)
Let's compute the integral u1·v2 + ∫(u1'·v2)dx: x·sin(x) -∫(sin(x))dx
x·sin(x) + cos(x)
Let's evaluate over the interval [0, 1]: (1·sin(1) + cos(1)) -(0·sin(0) + cos(0))
sin(1) + cos(1) + 0·sin(0) -cos(0)
sin(1) + cos(1) + 0 -1
sin(1) + cos(1) -1
The approximate value of: cos(1) + sin(1) -1 is:
0.5403 + 0.8415 -1
1.3818 -1
0.3818
Result:   cos(1) + sin(1) -1
▷▷Numeric value:  0.3818