cos(π/4-α)＝√2/4→(√2/2)(cosα+sinα)＝√2/4→cosα+sinα＝1/2.sin(π/4+α)＝(√2/2)(cosα+sinα)＝√2/4.(cosα+sinα)²＝1/4→sin2α＝-3/4.∴sin2α/sin(π/4+α)＝(-3/4)/(√2/4)＝-3√2/2....