y=sinx+cosx
=√2*[sinx*(√2/2) +cosx*(√2/2)]
=√2*[sinx*cos(π/4) +cosx*sin(π/4)]
=√2*sin(x +π/4)
y=sinx+cosx可化成_____?A.2sin(x-π/4)；B.2sin(x+π/4)； C.√2sin(x-π
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