解；
x∈[π/2,π]
x+π/4∈[3π/4,5π/4]
∵sin(x+π/4)=1/3
∴cos(x+π/4)=-2√2/3
∴sinx
=sin(x+π/4-π/4)
=sin(x+π/4)cosπ/4-cos(x+π/4)sinπ/4
=√2/2(1/3-2√2/3)
=√2/6-2/3
=(√2-4)/6用你的方法为什么我算出来是(√2 加4)/6是的，是加的不好意思