I don't know how to write the following problem: f(x)=2x^3-​15.4x^2+2.​7x+2.25 - Determine the area under f(x) on the interval [-1,8]. Use the zeros rounded to one decimal

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Meghan van Rooyen
Meghan van Rooyen 2021-11-30
回答： DGM 2021-11-30
f(x)=2x^3-15.4x^2+2.7x+2.25 - Determine the area under f(x) on the interval [-1,8]. Use the zeros rounded to one decimal.
zero points are: x=-0.3, x=0.5, x=7.5

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回答（2 个）

DGM
DGM 2021-11-30
Ran in:
This can all be done symbolically easily enough
xrange = [-1 8];
syms x
f = 2*x^3 - 15.4*x^2 + 2.7*x + 2.25;
area = int(f,x,xrange)
area = 
double(area)
ans = -480.6000
fplot(f,xrange)
grid on
but why would the zeros be needed? Is that just a confusing way of saying "integrate abs(f)"?
absarea = int(abs(f),x,xrange)
absarea = 
double(absarea)
ans = 512.9550
Yongjian Feng
Yongjian Feng 2021-11-30
Area under f(x) basically is just the definite integral of f(x) within the range, right?
You know how to use matlab to do integration?

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