(tan15)/(1-(tan15)^2),

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(tan15)/(1-(tan15)^2),(tan15)/(1-(tan15)^2),(tan15)/(1-(tan15)^2),原式=(sin15/cos15)/(1-sin15^2/cos15^

(tan15)/(1-(tan15)^2),
(tan15)/(1-(tan15)^2),

(tan15)/(1-(tan15)^2),
原式=(sin15/cos15)/(1-sin15^2/cos15^2)
上下乘cos15^2
=sin15cos15/(cos15^2-sin15^2)
由倍角公式
=1/2*sin30/(cos30)
=(1/4)/(√3/2)
=√3/6

(tan15)/(1-(tan15)^2)
=1/2×(2tan15)/(1-(tan15)^2)
=1/2×tan30
=1/2×√3/3
=√3/6

1-(tan15)^2=2(tan15)/tan30=2√3tan15
(tan15)/(1-(tan15)^2)=√3/6