1) The expression is incomplete and does not make sense as written. The trigonometric functions are not applied correctly.

2)
((1+cos)/sin) * (1 - cos/sin)
= (1 + cos) / sin - cos / sin
= (1 + cos - cos) / sin
= 1 / sin
= csc

The simplified expression is csc(x).

3)
(1 - cos^2)(90) / (cos + 4)
= sin^2(90) / (cos + 4)
= 1 / (cos + 4)
= 1 / (cos(90) + 4)
= 1 / (0 + 4)
= 1 / 4

The final simplified expression is 1 / 4.