Suppose [tex]f[/tex] is an even function and [tex]\int\limits^7_{-7} {f(x)} \, dx =18[/tex].
a. Evaluate [tex]\int\limits^7_0 {f(x)} \, dx[/tex]
b. Evaluate [tex]\int\limits^7_{-7} {xf(x)} \, dx[/tex]