1/2ab(SinC) (where a and b are two sides, and C is the angle in between them)
You asked about a right angled triangle. Assuming you wanted to know if C is allowed to be a right angle, which is 90, we would write:
1/2ab(Sin90)
We can simplify Sin90 straight away, because it is a number. It equals 1. So you are left with
1/2ab(1) = 1/2ab
I'd just like to note that your question isn't very clear. You've mentioned a right angled triangle (which should be 1/2(base x perpendicular height)), whereas 1/2abSinC works with any angle in a triangle (not just the right angle - it can work with the others provided you have the correct side lengths).