如题
sin(π/2+x)=-√5/5
cosx=-√5/5
sinx = 2√5/5
[(cosx)^3 +sinx] /cos(x-π/4)
=[(cosx)^3 +sinx] /[ (√2/2)(cosx+sinx) ]
=√2[(cosx)^3 +sinx] /(cosx+sinx)
=√2[ (-√5/5)^3 +2√5/5] /(-√5/5+2√5/5)
=√2[ -√5/25 +2√5/5] /(-√5/5+2√5/5)
=√2[ 9√5/25] /(√5/5)
=(9/5)√2
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