高一数学问题！谢谢！

(1)
sin(3π/4+β-π/4+α)
=sin(π/2+α+β)
=-cos(α+β)

cos(3π/4+β)=-12/13
cos(π/4-α)=3/5

sin(3π/4+β-π/4+α)
=cos(π/4-α)sin(3π/4+β)-sin(π/4-α)cos(3π/4+β)
=(5/13)*(3/5)-(-4/5)*(-12/13)
=-33/65

(2)
当x=0,y=1时，f(1/2)=1-sin a;
当x=1,y=0时，f(1/2)=sin a;
所以1-sin a = sin a;
sin a = 1/2;
所以 a = 30度；
所以f(1/2) = 1/2;
同理当x=0,y=1/2时，
f(1/4)=1/2-sin a /2;
所以f(1/4)=1/4;

设α属于（0，π/2),函数f(x)的定义域为[0,1]且f（0）=0，f（1）=1，当x大于等于y时，有f（x+y/2)=f(x)sinα+(1-sinα)f(y)
求f(1/2)和f（1/4