X x (25 - 1) = 25 x (23 +1)

X x 24= 25 x 24

X x 25 = 24 : 24

X x 25 = 1

       X = 25 : 1

       X = 25

a) A={x=3n|}

b) B={x=5n|}

c) C={x=10n|}

d) D={x=4n+1|

danh từ

9-1-2-4-1x9x9

=(9-(1+2+4+1))x9x9

=9x9

=81

I fall out of bed at night.