# Thread: [SOLVED] evaulating difinite integral???

1. ## [SOLVED] evaulating difinite integral???

Integrate [2xdx] from (1 to 2 )

ans = x square ( from 1 to 2)

evaulating from 1 to 2

process 1 : x square from ( 1 to 2 ) = 2 square - 1 square = 3

process 2: x square from ( 1 to 2 ) = [x*x ] from ( 1 to 2 )
= (2-1)*(2-1) = 1*1 = 1

which process is the correct one........really confused here????

thanky u for helping

2. Originally Posted by crb
Integrate [2xdx] from (1 to 2 )

process 1 : x square from ( 1 to 2 ) = 2 square - 1 square = 3

process 2: x square from ( 1 to 2 ) = [x*x ] from ( 1 to 2 )
= (2-1)*(2-1) = 1*1 = 1

which process is the correct one........really confused here????

thanky u for helping
$\int_1^2 2xdx = [x^2]^2_1 = 2^2 - 1^2 = 4-1 = 3$

3. thank u for helping out........but could u explain why the second one is incorrect?

4. Originally Posted by crb
could u explain why the second one is incorrect?
Consider this.
$\left. {\left( {x \cdot x} \right)} \right|_1^2 = \left( {2 \cdot 2} \right) - \left( {1 \cdot 1} \right) = 3$

5. thank you...very much