# Homework Help: Integration of sine

1. Oct 21, 2009

### ilikeicetea

1. The problem statement, all variables and given/known data
what is the integration of 1/2 sin y dy from 0 to pie/2

2. Relevant equations
i know sin y = -cos y (integration)

3. The attempt at a solution
from 1/2 sin y dy to (1/2) -cos y then i plot pie/2 and 0
i got (1/2) [-cos (pie/2) - (-cos 0)] = 0, but the answer is 1/2
i mean -cos (pie/2) = -1 & cos 0 = 1

Thank you for helping

2. Oct 21, 2009

### Staff: Mentor

Error in next line. BTW, the name of the Greek letter is pi, not pie. Pie is something you can eat.
(1/2)[-cos (pi/2) - (-cos 0)] != 0

3. Oct 21, 2009

### ilikeicetea

i forgot to add this, im trying to find out why the answer is 1/2 and not 0.

4. Oct 21, 2009

### Staff: Mentor

See post 2. I identified the line where you went wrong.

5. Oct 21, 2009

### ilikeicetea

but i though the integration of sin y is -cos y?

6. Oct 21, 2009

### Staff: Mentor

I'm not questioning that. Did you read post 2?

7. Oct 21, 2009

### Rohit Mallya

integration of 1/2sin(y) dy from 0 to pie/2=1/2[-cos(y)] from 0 to pie/2
=1/2{-cos(pie/2)-[-cos(0)]}
=1/2{0+1}
=1/2 [bcoz cos(0)=1 & cos(pie/2)=0]

8. Oct 21, 2009

### ilikeicetea

k, i got it, i put cos (pi/2) in my calculator but came out to be .9996, so that's why i didn't get the right answer.

edit. just know why, cause i have the mode under deg so that's why my answer is all mess up.

thanks everybody