If /6 /4 ( (x- 3 ) (x+ 3 )+1 )dx = e ( 3-1 ), then 9 2 is equal to .
Answer
12
Solution
(B - A) = A B + 1 A - B, take A = x - 3 and B = x + 3, so B - A = 2 3 and 2 3 = - 1 3. Hence
A B + 1 = - 1 3 ( A - B )
I = - 1 3 /6 /4 [ (x - 3 ) - (x + 3 ) ]dx
= - 1 3 [ e | (x - 3 ) (x + 3 ) | ] /6 /4
At x = 4 the ratio is 15 105 = 3 - 1 3 + 1 = 2 - 3, and at x = 6 it is 30 90 = 12, so
I = - 1 3 e (2 (2 - 3 ) ) = - 1 3 e ( 3 - 1 )2 = - 2 3 e ( 3 - 1 )
∴ = - 2 3 and 9 2 = 9 43 = 12
Answer: 12