You have to find the aera between the following functions and on (because curves meet for ).
By a symmetry the aera of the region is
And you obtain :
And he multiplied by 2 because it is symmetric. The area from -1 to 0 is the same as the area from 0 to 1- to find the area from -1 to 1, find the area from 0 to 1 and multiply by 2.