Simple integration

2010-05-22 11:03 pm
Integrate
∫[from −2 to −4]√(x²−4) dx

Hence, show that






4√3+2ln(2−√3)



∫[from −2 to −4]

√(x²−4)

dx ≤ −

4√3+2ln(2−√3)


8



64

Evaluate





∫[from −2 to −4]

√(x²−4)

dx



Check whether the answer satisfy the above inequality.
更新1:

Sorry the limit should be from -4 to -2

更新2:

One interesting thing to ask is that why we are not using principal values of arcsecant, i.e. x=-2 =>pi x=-4 =>2pi/3 but we should use x=-2 =>pi x=-4 =>2pi/3 instead in doing transformation of boundaries?

更新3:

Correction: One interesting thing to ask is that why we are not using principal values of arcsecant, i.e. x=-2 =>pi x=-4 =>2pi/3 but we should use x=-2 =>pi x=-4 =>4pi/3 instead in doing transformation of boundaries?

回答 (1)

2010-05-23 1:22 am
✔ 最佳答案
Please see the following:

圖片參考:http://img231.imageshack.us/img231/8995/94644717.png


2010-05-22 17:23:02 補充:
http://img231.imageshack.us/img231/8995/94644717.png

2010-05-22 17:45:22 補充:
Correction J=θ/4 - (sin 2θ)/8 + C
Integral = π/4 - π/3 - (sin2π)/8+[sin(8π/3)]/8=-0.1535

2010-05-22 19:03:48 補充:
Because I take sqrt(x^2 - 4) as +2tanθ
when x=-4, secθ=-2 and tanθ = +sqrt(3) => θ=4π/3
If θ=2π/3 then tanθ=-sqrt(3), then sqrt(x^2-4)=-2tanθ
I missed the square root sign in line 3 for tanθ


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