=(sin15+cos15)²/(sin²15-cos²15)——分子分母乘以(sin15+cos15) 5
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（1）4tan75 /（1-tan75）= 4sin75 /（cos75-sin75）
= 4cos15 /（SIN15-cos15）= 4cos15（SIN15 + cos15）/（2罪15-COS 2 15）
> = - （4cos15sin15 4 COS 2 15）/ cos30
= - [2sin30 2（1 + cos30）] / cos30
= - （1 + 2√3）* 2 /√3 = -2（1 +√3）
（2）（2sinπ/17cosπ/17*cos2π/17*cos4π/17*cos8π/17）/2sinπ/17
=（sin2π/17cos2π/17 *cos4π/17*cos8π/ 17）/2sinπ/17
=（2sin2π/17cos2π/17*cos4π/17*cos8π/17）/4sinπ/17
=sin4π/17*cos4π/17* cos8π/17）/4sinπ/ 17
=2sin4π/17*cos4π/17*cos8π/17）/8sinπ/17
=sin8π/17*cos8π/17/8sinπ/17=sin16π/17/ 16sinπ/17
=sinπ/17/16sinπ/17= 1/16
= 4cos15 /（SIN15-cos15）= 4cos15（SIN15 + cos15）/（2罪15-COS 2 15）
> = - （4cos15sin15 4 COS 2 15）/ cos30
= - [2sin30 2（1 + cos30）] / cos30
= - （1 + 2√3）* 2 /√3 = -2（1 +√3）
（2）（2sinπ/17cosπ/17*cos2π/17*cos4π/17*cos8π/17）/2sinπ/17
=（sin2π/17cos2π/17 *cos4π/17*cos8π/ 17）/2sinπ/17
=（2sin2π/17cos2π/17*cos4π/17*cos8π/17）/4sinπ/17
=sin4π/17*cos4π/17* cos8π/17）/4sinπ/ 17
=2sin4π/17*cos4π/17*cos8π/17）/8sinπ/17
=sin8π/17*cos8π/17/8sinπ/17=sin16π/17/ 16sinπ/17
=sinπ/17/16sinπ/17= 1/16
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