How do you find the area of the region bounded by the curves #y=|x|# and #y=x^2-2# ?

1 Answer
Sep 25, 2014

This is a definite integral problem

First we need to find the intersections of these 2 functions by setting them equal to each other.

#|x|=x^2-2#

This has to be split up into 2 equations.

#x=x^2-2# AND #-x=x^2-2#

FIRST
#x=x^2-2#
#x^2-x-2=0#
Factor
#(x-2)*(x+1)=0#
#x-2=0#
#x=2#

#x+1=0#
#x=-1#

SECOND
#-x=x^2-2#
#x^2+x-2=0#
Factor
#(x+2)*(x-1)=0#
#(x+2)=0#
#x=-2#

#(x-1)=0#
#x=1#

The interval is from #[-2,2]#

The function #|x|# is greater than the function #x^2-2# over the interval [-2,2].

#int_(-2)^(2)|x|-(x^2-2)dx=int_(-2)^(2)|x|-x^2+2dx#

#=int_(-2)^(2)|x|dx-int_(-2)^(2)x^2dx+int_(-2)^(2)2dx#

Note: |x| is an even function and symmetric about the #y#-axis so make this function easier to manage we can assume x>0 and double the area found by multiplying it by 2 and changing the boundaries from 0 to 2.

#=2*int_0^(2)xdx-int_(-2)^(2)x^2dx+int_(-2)^(2)2dx#

#=2*[x^2/2]_0^2 -1* [x^3/3]_(-2)^2+1*[2x]_(-2)^2#

#=2*[(2)^2/2-(0)^2/2] -1* [(2)^3/3-(-2)^3/3]+1*[2(2)-2(-2)]#

#=2*[2-0] -1* [8/3+8/3]+1*[4+4]#

#=2*[2] - [16/3]+[8]#

#=[4] - [16/3]+[8]#

#=[12/3] - [16/3]+[24/3]#

#= [-4/3]+[24/3]#

#= [20/3]#

#= 6 2/3 or 6.6667#