The shell method uses the formula #2pi int x*f(x) color(white)(.) dx# with #f(x)# being our function and #x# as our radius
#* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * #
#y=x#
#2pi int x * x color(white)(.)dx#
#2pi int x^2 color(white)(.) dx#
#2pi xx x^(2+1)/(2+1)# via power rule
#2pi xx x^3/3#
#(2 pi x^3)/3#
#* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * #
#y = -x/2#
#2pi intx * -x/2 color(white)(.)dx#
#(-2pi)/2 int x^2color(white)(.) dx#
#-pi intx^2color(white)(.)dx#
#(-pi x^3)/3#
#* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * #
#y = x^2#
#2pi int x * x^2 color(white)(.) dx#
#2pi int x^3 color(white)(.) dx#
#2pi xx x^4/4#
#(pix^4)/2#
#* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * #
#y = 2-x#
#2pi int x(2-x) color(white)(.) dx#
#2pi int 2x - x^2 color(white)(.) dx#
#2pi int2x color(white)(.) dx - 2pi int x^2 color(white)(.) dx#
#4pi intx color(white)(.) dx - (2pi x^3)/3#
#4pi x^2/2 - (2pix^3)/3#
#2pi x^2 - (2pix^3)/3#
#(3(2pix^2))/3 - (2pix^3)/3#
#(6pix^2 - 2pix^3)/3#
#* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * #