Ti-89 Differing Answers from Integration

[jpreher]

I am running into an interesting problem on my ti-89 and was wondering if anyone could explain the reason for the following.

I am attempting to solve the following:
M=\int_{x}^{y}sin(\theta )*(r-a*cos(\theta ))d\theta

r = 0.14
a = 0.09

where,
x = 0 deg
y = 120 deg

The calculator gives me an answer of
M = 10.09838
This answer is incorrect, so I verified that the ti-89 was in degrees (it was) and decided to try the problem in rads instead to see if it is still incorrect.

now where,
x = 0 rad
y = 2*pi/3

I get a correct answer of
M = 0.17625

What is going on here?

 

[jedishrfu]

your integral as written is radian based.
take your 10. 098 answer and divide by 57 degrees (1 rad) and you would get the second answer