Saturday, October 25, 2014

Evaluate definite integral of f(x)=minim{x^2,3x-2} for x=0 to x=2.

Before evaluating the definite integral, we'll apply the
rule of minimum to the function f(x).


minim m(x) =
min{u(x),v(x)} is:


- u(x), for
u(x)<v(x)


- v(x), for
u(x)>v(x)


We'll apply the rule of min to the
function f(x):


- x^2, for x^2<3x-2 <=>
x^2 - 3x + 2 < 0


- 3x-2, for x^2>3x-2
<=> x^2 - 3x + 2 > 0


We'll calculate
the roots of x^2 - 3x + 2 to verify where the expression is positive and where it's
negative.


 It is obvious that the roots of the expression 
x^2 - 3x + 2 are 1 and 2.


x1 + x2 = 3 =
S


x1*x2 = 2 = P


1 + 2 =
3


1 * 2 = 2


The xpression is
negative over the interval [1,2] and it is positive over the intervals (-inf.,1) U
(2,+inf.).


Now, we'll calculate the definite
integral.


Int f(x) dx = Int 1 + Int
2


Int 1 = Int f(x)x from x = 0 to x =
1


Int 2 = Int f(x) dx from x = 1 to x =
2


Int 1 = Int (3x-2)dx = Int 3xdx - 2Int
dx


Int 1 = 3x^2/2 - 2x


Int 1 =
F(1) - F(0)


F(1) - F(0) = 3/2 - 2 =
-1/2


Int 1 =
-1/2


Int 2 = F(2) -
F(1)


Int 2 = Int x^2dx


Int 2 =
x^3/3


F(2) - F(1) = 2^3/3 -
1^3/3


F(2) - F(1) = 8/3 - 1/3 =
7/3


Int 2 =
7/3


Int f(x) dx = Int 1 + Int
2


Int f(x) dx = Int 1 + Int
2


Int f(x) dx = -1/2 + 7/3


Int
f(x) dx = (-3 + 14)/6


Int f(x) dx =
11/6

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