วันพุธที่ 9 เมษายน พ.ศ. 2557

Calculus Integration


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# h3macaar1
Calculate the area enclosed by the curve y = x2+1, the y-axis
and the lines, y=2,y=3 for the portion in the first quadrant only.
(Problem credited by O-Level --Marshal Cavendish)




Strategy - the rule "Must have" of Mr.Zhang ®
Find the area ;
  → (1)
To calculate area A, x must be expressed in terms
of y for the intregation.

Solution   We have ;
y = x2 + 1
x2 = y - 1
x = (y-1) 1/2
We bring the equation(1) to find the required area;

=

=

=
2
3
(2)3/2   -
2
3
(1)3/2
=
2
3
(2√2)   -
2
3
      =
2
3
(2√2 - 1)
.
Ans.    The area is 
2
3
(2√2 - 1) units2


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