Sin -270 different from sin - 90 exact and aprox values?

[Senjai]

1. The problem statement, all variables and given/known data

Homework related question:Write the exact value of sin(-270)

3. The attempt at a solution

I had this same question before but to write it in approximate value. for an aprox value i simply just plug it into my calculator and get: 1. Pretty exact for an approximate value. When i solve it the exact way. (No calculator) i determine that the Reference angle for -270 degrees is -90 degrees. then i sin -90 degrees and get -1. The answer is 1. I don't understand.

[Mark44]

1. The problem statement, all variables and given/known data

Homework related question:Write the exact value of sin(-270)

3. The attempt at a solution

I had this same question before but to write it in approximate value. for an aprox value i simply just plug it into my calculator and get: 1. Pretty exact for an approximate value. When i solve it the exact way. (No calculator) i determine that the Reference angle for -270 degrees is -90 degrees. then i sin -90 degrees and get -1. The answer is 1. I don't understand.
The reference angle for -270 degrees is +90 degrees. sin(90 deg.) = 1, exactly.

[Senjai]

Oh! Ref angles are always positive.. sorry.. Thanks for your time!!