Taking x+π/4 as a whole, the monotonic increasing range is -3π/4+2kπ, π/4+2kπ.

2. The image of function y=3cos(2x+φ) is symmetrical about the center of point (3 π/4,0), so

3cos(2*3π/4+φ)=0, so 3π/2+φ=π/2+kπ, so φ=-π+kπ, when k=0, φ is at least 0.

3. Go upstairs together. The key is to compare the size of abc,

The analysis shows that their absolute values tan 5/7 π >; cos 5/7π& gt； sin5/7π

∴c & gt； B>a (According to monotonicity, you only need to compare the size of the domain. )