tan1°=tan(90°-89°)=ctan89°
tan2°=ctan88°
.
tan44°=ctan46°
tan45°=1
所以,
tan1°×tan2°×tan3°×tan4°×tan5°×……×tan87°×tan88°×tan89°
=tan89°×ctan89°×tan88°×ctan88°×...tan46°×ctan46°×tan45°
=1×1×1×...×1×1=1 tan1°=tan(90°-89°)=ctan89°
tan2°=ctan88°
.
tan44°=ctan46°
tan45°=1
所以,
tan1°×tan2°×tan3°×tan4°×tan5°×……×tan87°×tan88°×tan89°
=tan89°×ctan89°×tan88°×ctan88°×...tan46°×ctan46°×tan45°
=1×1×1×...×1×1=1