Question

求值：① sin47°-sin17°cos30° cos17° ② 1 sin10° - ...

求值：① sin47°-sin17°cos30° cos17° ② 1 sin10° - 3 cos10° ．

Answer 1

①式子= sin(17°+3 0 ° )-sin17°cos30° cos17° = cos17°sin30° cos17° =sin30°= 1 2 ； ②式子= cos1 0 ° - 3 sin1 0 ° sin10°cos1 0 ° = 2( 1 2 cos1 0 ° - 3 2 sin1 0 ° ) 1 2 sin20° = 2sin2 0 ° 1 2 sin20° =4．