如图,数学,高数,求这个定积分?
2个回答
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1-sin2x =1-2sinxcosx =sin²x-2sinxcosx+cos²x =(sinx-cosx)²
则: 根号下(1-sin2x)=|sinx-cosx|
原式=∫(π/2,0)|sinx-cosx|dx
=∫(π/4,0)(cosx-sinx)dx+∫(π/2,π/4)(sinx-cosx)dx
=(sinx+cosx)|(π/4,0)+(-cosx-sinx)|(π/2,π/4)
=(sinx+cosx)|(π/4,0)-(cosx+sinx)|(π/2,π/4)
=(sinπ/4+cosπ/4-sin0-cos0)-(cosπ/2+sinπ/2-sinπ/4-cosπ/4)
=(√2/2+√2/2-0-1)-(0+1-√2/2-√2/2)
=(√2-1)-(1-√2)
=2√2-2
则: 根号下(1-sin2x)=|sinx-cosx|
原式=∫(π/2,0)|sinx-cosx|dx
=∫(π/4,0)(cosx-sinx)dx+∫(π/2,π/4)(sinx-cosx)dx
=(sinx+cosx)|(π/4,0)+(-cosx-sinx)|(π/2,π/4)
=(sinx+cosx)|(π/4,0)-(cosx+sinx)|(π/2,π/4)
=(sinπ/4+cosπ/4-sin0-cos0)-(cosπ/2+sinπ/2-sinπ/4-cosπ/4)
=(√2/2+√2/2-0-1)-(0+1-√2/2-√2/2)
=(√2-1)-(1-√2)
=2√2-2
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