a . 3.15 – 4^2 . 1^2019 + 5^2 b. ( 2^78 + 2^79+ 2^80) : ( 2^75+2^76+2^77) c. ( 12x – 140) . 5^14 = 4. 5^10

 a.  3 . 15 – $4^{2}$ . $1^{2019}$ + $5^{2}$ 

    = 45 – 16 . 1 + 25

    = 45 – 16 + 25

    = 29 + 25

    = 54  

 b.  ( $2^{78}$ + $2^{79}$ + $2^{80}$ ) ÷ ( $2^{75}$ + $2^{76}$ + $2^{77}$ ) 

    = (  $2^{78}$  + $2^{78}$ . 2 + $2^{78}$ . $2^{2}$ ) + ( $2^{75}$ + $2^{75}$ . 2 + $2^{75}$ . $2^{2}$ ) 

    = [ $2^{78}$ . ( 1 + 2 + $2^{2}$ ] + [ $2^{75}$ . ( 1 + 2 + $2^{2}$ ) ] 

    = $2^{78}$ ÷  $2^{75}$ 

    = $2^{3}$

    = 8

Ý c số to quá b ạ