Question

(3 la puterea 21-3 la puterea20- 3 la puterea19):(9 la puterea8*5)

Answer 1

$( {3}^{21} - {3}^{20} - {3}^{19} ) \div ( {9}^{8} \times 5)$

$=[ {3}^{19}( {3}^{2} - 3 - 1) ] \div [ {( {3}^{2} )}^{8} \times 5 ]$

$= [ {3}^{19} (9 - 3 - 1)] \div ( {3}^{2 \times 8} \times 5)$

$= ( {3}^{19} \times 5) \div ( {3}^{16} \times 5)$

$= ( {3}^{19} \div {3}^{16}) \times( 5 \div 5)$

$= {3}^{19 - 16} \times 1$

$= {3}^{3} \times 1$

$= {3}^{3}$

$= 27$