Bài tập 25.Cho a,b,c là ba số tự nhiên .Biết a+5=b+7=c+10 ,hãy so sánh a , b , c.
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*) a + 5 = b + 7
⇒ a = b + 7 - 5
⇒ a = b + 2
⇒ a > b (1)
*) b + 7 = c + 10
⇒ b = c + 10 - 7
⇒ b = c + 3
⇒ b > c (2)
Từ (1) và (2) ⇒ a > b > c
a+5=b+7=c+10
=>a+5=b+7 và b+7=c+10
=>a-b=2>0 và b-c=10-7=3>0
=>a>b và b>c
=>a>b>c
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a}n,n+1,n+2
b]n-1,n,n+1
9]
A=[11,12,13,14,........................................................,997,998,999
B=(1,3,5,7,9,...................................................................................,999]
C=[0,2,4,6,8,..........................................................,2014]
1.
\(A=\left\{1,2,3,4,5\right\}\)
\(A=\left\{x\in N^{\circledast}|x\le5\right\}\)
2.
a)Số phần tử là: \(\left(51-13\right)\div2+1=20\)( p/t)
b)Số phần tử là: \(\left(39-8\right)+1=32\)( p/t)
c)Số phần tử là vô cực
d)Số phần tử là 1
a+5=b+7=c+10<=>a=b+2=c+5
=>a>b>c
đáp án: a < b < c
vd:
a => 1 + 5 = 6
b => 1 + 7 = 8
c => 1 + 10 = 11
dễ thấy : a < b < c