# Thread: Find Value of Sin C

1. ## Find Value of Sin C

In triangle ABC, sin (A + B) = 3/5.
What is the value of sin C?

2. Originally Posted by magentarita
In triangle ABC, sin (A + B) = 3/5.
What is the value of sin C?
In triangle $ABC, C = 180^\circ - (A + B)^\circ$

So use the formula

$\sin{C} = \sin{[180^\circ - (A + B)^\circ]} = \sin{180^\circ}\cos{(A + B)^\circ} - \cos{180^\circ}\sin{(A + B)^\circ}$

and solve for $\sin{C}$.

3. ## Values for...

Originally Posted by Prove It
In triangle $ABC, C = 180^\circ - (A + B)^\circ$

So use the formula

$\sin{C} = \sin{[180^\circ - (A + B)^\circ]} = \sin{180^\circ}\cos{(A + B)^\circ} - \cos{180^\circ}\sin{(A + B)^\circ}$

and solve for $\sin{C}$.
I can plug and chug but what are the values of A and B? How do I find the values of A and B. Do I need the values of A and B?

4. You don't need them.

What does $\sin{180^\circ}$ equal?

Once you've found that, what does $\sin{180^\circ}\cos{(A + B)^\circ}$ equal?

What does $\cos{180^\circ}$ equal?

Since you're GIVEN the value of $\sin{(A + B)^\circ}$, what is $\cos{180^\circ}\sin{(A + B)^\circ}$?

5. ## ok

Originally Posted by Prove It
You don't need them.

What does $\sin{180^\circ}$ equal?

Once you've found that, what does $\sin{180^\circ}\cos{(A + B)^\circ}$ equal?

What does $\cos{180^\circ}$ equal?

Since you're GIVEN the value of $\sin{(A + B)^\circ}$, what is $\cos{180^\circ}\sin{(A + B)^\circ}$?
I now understand what you mean.