#bar x = (int_0^2 x * y \ dx)/(int_0^2 y \ dx)#
# = (int_0^2 4 x - x^3 \ dx)/(int_0^2 4 - x^2 \ dx)#
# = ([ 2 x^2 - x^4/4 ]_0^2)/([ 4x - x^3/3 ]_0^2) = (4)/(16/3) = 3/4 = 0.75#
#bar y = (int_0^2 y/2 * y \ dx)/(int_0^2 y \ dx)#
# = (1/2int_0^2 16 - 8x^2 +x^4 \ dx)/(16/3)#
# = 1/2 ( [ 16x - 8/3x^3 +x^5/5 ]_0^2)/(16/3)#
#= 1/2* (32 - 64/3 + 32/5)/(16/3) = 8/5 = 1.6#