Midpoint Formula: (

,

)
Midpoint = (

,

)
Midpoint = (

,

)
Midpoint = (

, -4)
So, the midpoint of the endpoints (-4,-3) and (7,-5) is (

, -4).
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Volume is defined as area of the base*the hight.
In this question the base is the traingles.
Area of a triangle is base*hight/2, so it 8*6/2= 24
Volume is 24*8(hight)=192
So the answer is 192cm^3
To get the extrema, derive the function.
You get y' = 2x^-1/3 - 2.
Set this equal to zero, and you get x=0 as the location of a critical point.
Since you are on a closed interval [-1, 1], those points can also have an extrema.
Your min is right, but the max isn't at (1,1). At x=-1, you get y=5 (y = 3(-1)^2/3 -2(-1); (-1)^2/3 = 1, not -1).
Thus, the maximum is at (-1, 5).