a) $5.4^x+4^{2+x}=336$

$5.4^x+4^2.4^x=336$

$4^x.(5+4^2)=336$

$4^x.21=336$

$4^x=336:21$

$4^x=16$

$4^x=4^2$

$x=2$.

Vậy $x=2$.

b) Các bội của $11$ là: $0;11;22;33;44;55;\dots$

Mà $10<x<40$

Vậy $x\in \{11;22;33\}$.

a)$571+216+129+124$

=(571+129)+(216+124)

=700+340

=1040

b)27x74+26x27-355

=27x(74+26)-355

=2700−355

=2345

c)100:{250:[450-(4.5³-2².25)]}

=100:{250:[450-(500-400)]}

=100:{250:[450-50]}

=100:{250:50}

=100:5

=20

Bài 1

a) Các số đó là:320;4914;90

b) Các số đó là:320;90

c) Các số đó là:90;4914;543

d) Các số đó là:90

Da Lat city is one of the famous tourist cities of Vietnam. Looking down from above, Da Lat is a picture. The landscape here is extremely diverse and rich. In the morning you can take pictures with the ancient castles, in the afternoon move to a modern cafe or take a walk in the colorful flower gardens. The weather in Dalat is very cool. You can wear your favorite clothes. Tourists come here a lot. The weather of Da Lat is very interesting, it will change according to the time of day. If you pay attention, you will see that one day in Da Lat has all the weather of four seasons. It will be foggy in the morning, sunny in the afternoon. There will be occasional showers. As it gets dark, the temperature will drop lower. Thanks to favorable weather, Da Lat is always full of flowers. Every year, there will be flower festivals here. There are many rare flowers on display on this occasion. The beauty of Dalat cannot be described in a few sentences. If you have time, come to Da Lat and experience it.