Calc II: Help Solving this Integral

  • Thread starter Thread starter Hertz
  • Start date Start date
  • Tags Tags
    Integral
Hertz
Messages
180
Reaction score
8

Homework Statement



\int \frac{\sqrt{9 - x^2}}{x} dx

2. The attempt at a solution

x = 3sin(u)
dx = 3cos(u)du
u = arcsin(x/3)

\int \frac{3\sqrt{cos(u)^2}}{3sin(u)} 3cos(u)du

3 \int \frac{cos(u)}{sin(u)} cos(u)du

Don't really see anywhere to go from here. Apologies if the work is hard to follow, I cut out a few steps because inputting equations is a real pain in my opinion.
 
Physics news on Phys.org
Hertz said:

Homework Statement



\int \frac{\sqrt{9 - x^2}}{x} dx

2. The attempt at a solution

x = 3sin(u)
dx = 3cos(u)du
u = arcsin(x/3)

\int \frac{3\sqrt{cos(u)^2}}{3sin(u)} 3cos(u)du

3 \int \frac{cos(u)}{sin(u)} cos(u)du

Don't really see anywhere to go from here. Apologies if the work is hard to follow, I cut out a few steps because inputting equations is a real pain in my opinion.

Write cos2(u) as 1 - sin2(u), and then split into two integrals.
 
Mark44 said:
Write cos2(u) as 1 - sin2(u), and then split into two integrals.

Ah! Thank you, I'll give it a try
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...

Similar threads

Back
Top