sin(a-b)cos a -cos(b-a)sin a= -[sin(b-a)cos a + cos(b-a) sina]= - sin(b-a + a)= -sinb=> sin b = -3/5=> cos b = -4/5sin(b+5π/4) = sin b cos(5π/4) + cos b sin(5π/4) = -3/5 * (-√2/2) - 4/5 * (-√2/2)...后面的题也告诉我，好么？其他的题什么意思？没看明白