Can someone show this simplification in steps im lost on how they got the final answer?
The question is using finite approximation estimate the area under the graph of f(x)=2x^2 and above the graph of f(x)=0 from x0=0 to xN=6 using lower sum 2 and 4 rectangles, and upper sum 2 and 4 rectangles. They show A=(3-0)f(0)+(6-3)f(3)...but my answer doesnt match. Can someone simplify this for me and show why/how?

Question

Can someone show this simplification in steps im lost on how they got the final answer?
The question is using finite approximation estimate the area under the graph of f(x)=2x^2 and above the graph of f(x)=0 from x0=0 to xN=6 using lower sum 2 and 4 rectangles, and upper sum 2 and 4 rectangles. They show A=(3-0)f(0)+(6-3)f(3)...but my answer doesnt match. Can someone simplify this for me and show why/how?

amistre64 · Answer

do you now how to take that area of a rectangle?

anonymous · Answer

that's the area equation right there that i filled in for the lower 2 rectangles of equal width, but i must be doing something wrong cause I'm not getting the answer 
 from that

amistre64 · Answer

lower 2 means 2 rectangles right?

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lower 4 is then 4 rectangles to fill the interval