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| 1. |
(sin 72 + cos 18) (sin 72 - cos 18) |
| Answer» \xa0(sin72° +\xa0cos18°)(sin72° −\xa0cos18°).= (sin2\xa072° –\xa0cos2\xa018°)= (sin2\xa072° –\xa0cos2\xa0(90° –\xa072°)\xa0=\xa0sin2\xa072° –\xa0sin2\xa072°= 0 | |