Tìm x :
5 + 10 = 30 - x
10 + 40 = 90 - x
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X x 10 x10 x10 x10 = 40000
X x 10000 = 40000
x = 40000 : 10000
x = 4
30 + x = 40 + 60
30 + x = 100
x = 100 - 30
x = 70
10 + 90 = 40 + x
100 = 40 + x
x = 100 - 40
x = 60
30+x=40+60
30+x=100
x=100-30
x=70
10+90=40+x
100 =40+x
100-40=x
60 =x
\(\frac{x+10}{90}+\frac{x+20}{80}+\frac{x+30}{70}+\frac{x+40}{60}+\frac{x+50}{50}=-5\)
<=> \(\frac{x+10}{90}+1+\frac{x+20}{80}+1+\frac{x+30}{70}+1+\frac{x+40}{60}+1+\frac{x+50}{50}+1=0\)
<=> \(\frac{x+100}{90}+\frac{x+100}{80}+\frac{x+100}{70}+\frac{x+100}{60}+\frac{x+100}{50}=0\)
<=> \(\left(x+100\right)\left(\frac{1}{90}+\frac{1}{80}+\frac{1}{70}+\frac{1}{60}+\frac{1}{50}\right)=0\)
<=> x + 100 = 0
<=> x = -100
Vậy x = -100
a) 43 x 27 + 43 x 13 + 43 x 68
= 43 x ( 27 + 13 + 68 )
= 43 x 108
= 43 x ( 100 + 8 )
= 43 x 100 + 43 x 8
= 4300 + 344
= 4644
b) 90 x 21 + 15 x 10 + 30 x 74
= 30 x 63 + 30 x 5 + 30 x 74
= 30 x ( 63 + 5 + 74 )
= 30 x 142
= 30 x ( 100 + 42 )
= 30 x 100 + 30 x 42
= 3000 + 1260
= 4260
( 50 + 50 ) x 90 + ( 5 + 1000 ) x10
= 100 x 90 + 1005 x 10
= 900 + 10050
= 10950
( 50 + 50 ) x 90 + ( 5 + 1000 ) x10 = 100 x 90 + 1005 x 10
900 + 10050 = 10950
a)5+10=30-x
=>15=30-x
=>x=30-15
=>x=15
b)10+40=90-x
=>50=90-x
=>x=90-50
=>x=40
\(5+10=30-x\)
\(15=30-x\)
\(x=15\)
\(10+40=90-x\)
\(50=90-x\)
\(x=40\)