Question

1) Tính bằng cách hợp lí nhất

a) 21x7²-11x7²+90x7²+49x125x16

b) (2^2+2^1+2^2+2^3) .2^0.2^1.2^2.2^3

 

 

Answer 1

a) 21x7²-11x7²+90x7²+49x125x16

= 21 x 49 - 11 x 49 + 90 x 49 + 49 x 125 x 16

= 49 x ( 21 - 11 + 90 + 125 x 16 )

= 49 x ( 21 - 11 + 90 + 2000 )

= 49 x 2100

= ( 50 - 1 ) x 2100

= 50 x 2100 - 2100

= 105 000 - 2100

= 102 900

Answer 2

b) (2²+2¹+2²+2³) . 2⁰.2¹.2².2³

= ( 4 + 2 + 4 + 8 ) . 1 . 2 . 4 . 8

= 18 . 8 . 8

= 144 . 8

= 1152

Answer 3

\(a)21\times7^2-11\times7^2+90\times7^2+49\times125\times16=21\times7^2-11\times7^2+90\times7^2+7^2\times125\times16=7^2\times\left(21-11+90+125\times16\right)=7^2\times2100=102900\)

\(\left(2^2+2^1+2^2+2^3\right)\times2^0\times2^1\times2^2\times2^3=\left(2^2\times2^0\right)+\left(2^1\times2^1\right)+\left(2^2\times2^2\right)+\left(2^3\times2^3\right)=4+\left(2^1\right)^2+\left(2^2\right)^2+\left(2^3\right)^3=4+2^2+2^4+2^9=4+4+16+512=536\)