First, we know that sin(39°)cos(21°) + cos(39°)sin(21°) can be simplified using the angle addition formula for sine:

sin(a + b) = sin(a)cos(b) + cos(a)sin(b)

Therefore, sin(39°)cos(21°) + cos(39°)sin(21°) can be rewritten as sin(39° + 21°) which equals sin(60°).

Finally, sin(60°) can be simplified using the unit circle or special triangle to get √3/2.

So, sin(39°)cos(21°) + cos(39°)sin(21°) simplifies to √3/2.