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不查表求值:[1+cos(π/5),1+cos(3π/5)].
∵cos(π/5)+cos(3π/5)=sin(2π/5)/[2sin(π/5)]+[sin(4π/5)-sin(2π/5)]/[2sin(π/5)]=1/2 ∴[1+cos(π/5),1+cos(3π/5)] =1+cos(π/5)+cos(3π/5)+cos(π/5)cos(3π/5) =1+1/2+[cos(4π/5)+cos(2π/5)]/2 =3/2+[-cos(π/5)-cos(3π/5)]/2 =5/4
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