# Integerating (1/((sinx)^2))

#### Geekchick

1. Homework Statement

25$$\int\frac{1}{sin^{2}x}$$dx

3. The Attempt at a Solution

I wasn't sure if I could change $$\frac{1}{sin^{2}x}$$ to Csc$$^{2}$$x but when I did I ended up with -25Cotx which when I checked the integral in my calculator and it was wrong. So now i'm lost...

Related Calculus and Beyond Homework Help News on Phys.org

#### Geekchick

FYI, the original problem was $$\int\frac{1}{x^{2}\sqrt{25-x^{2}}}$$dx I used trigonometric substitution to get to the problem above.

#### kbaumen

Well in an online integral table I found that $$\int \csc^2 ax dx = -\frac{1}{a} \cot ax + C$$ so you should probably come up with $$-\frac{cot(25x)}{25} + C$$.

#### yyat

-25Cot(x) is the integral of 25/sin^2(x), you can check it by computing the derivative.

#### Geekchick

Well did I go wrong before I got to the sin integral? because when I checked it against the original problem it didn't match.

#### Geekchick

Oh I did catch that it should be 1/25 not 25. But its still slightly off.

#### Dick

Homework Helper
Judging from what you've shown us, you used the substitution x=5*sin(u) to reduce the integral to (1/25) times the integral (1/sIn(u)^2)*du. That's fine. So you've got -cot(u)/25 as the integral. You still have to express that in terms of x.

#### Geekchick

I substituted $$\frac{\sqrt{25-x^{2}}}{x}$$ for cot So what I end up with is -$$\frac{\sqrt{25-x^{2}}}{25x}$$+c

#### Dick

Homework Helper
That looks fine to me.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving