sin(2a+270) can be simplified to -cos(2a), so the expression becomes:

1 - cos(2a - 270) + sin(2a + 270)

= 1 - cos(2a - 270) - cos(2a)

Now, using the angle subtraction formula for cosine, we have:

cos(2a - 270) = cos(270)cos(2a) + sin(270)sin(2a)
= 0 cos(2a) + 1 sin(2a)
= sin(2a)

Therefore, the expression simplifies to:

1 - sin(2a) - cos(2a)
= 1 - sin(2a) - cos(2a)

This is the final simplified form of the expression.