求解数学答案，急！

已知sin(x-派/4)=7倍的根号2/10，x属于（派/2,3倍的派/4）， 求sinx的值， 求cos(2x+派/3）的值。

sin(x-π/4)

=sinxcosπ/4-cosxsinπ/4

=√2/2(sinx-cosx)=7√2/10

sinx-cosx=7/5

(sinx-cosx) ^ =1-2sinxcosx=1-sin2x=49/25

sin2x=-24/25

x∈（π/2,3π/4),2x∈（π,3π/2)

cos2x=-7/25

而cos2x=1-2sin^x=-7/25

sin^x=16/25

sinx=4/5

cos(2x+π/3)

=cos2xcosπ/3-sin2xsinπ/3

=1/2cos2x-√3/2sin2x

1/2x(-7/25)-√3/2x(-24/25)

=-7/50+24√3/50

=(24√3-7)/50