(1）y=√（2sin^2x+cosx-1)
=√(2-2cos^2x+cosx-1)
-2cos^2x+cosx+1≥0
2cos^2x-cosx-1≤0
（2cosx+1）(cosx-1)≤0
-1/2≤cosx≤1
x∈[2kπ-2/3π,2kπ+2/3π]
(2)y=√[log2(1/sinx)-1]
log2(1/sinx)-1≥0
log2(1/sinx)≥1
0x∈[2kπ,2kπ+π]
16-x^2>0=>-4