hãy so sánh A và B
A=98/99 và B=98 nhân 99 cộng 1/98 nhân 99
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a,) a < b
b) a > b
c, a > b
Ko tính kết quả.Mình cam đoan luôn.
Chúc bạn học tốt `~<>
Monfan sub bạn cậu có thể trình bày ra cho tớ dc ko ?
98 <1
99
98.99+1 Vì 98.99+1 >98.99 nên 98.99+1 >1
98.99 98.99
Suy ra: 98 < 98.99+1
99 98.99
A= \(\frac{98}{99}\)< \(1\)
B= \(\frac{98.99+1}{98.99}\)=\(\frac{98.99}{98.99}+\frac{1}{98.99}\)=\(1+\frac{1}{98.99}\)> 1
=> A<1<B => A<B
Ta có:
99.99= (98+1) . 99 = 98.99+99
98.100 = 98.( 99+1) = 98.99 + 98
Do 98.99+99 > 98.99 + 98
=> 99.99 > 98.100
`A=3/4+8/9+.............+9999/10000`
`=1-1/4+1-1/9+,,,,,,,,,,+1-1/10000`
`=99-(1/4+1/9+.........+1/10000)<99-0=99`
`=>A<99`
\(C-D=\dfrac{\left(98^{99}+1\right)\left(98^{88}+1\right)-\left(98^{89}+1\right)\left(98^{98}+1\right)}{\left(98^{89}+1\right)\left(98^{88}+1\right)}\)
\(=\dfrac{98^{187}+98^{99}+98^{88}+1-98^{197}-98^{89}-98^{98}-1}{\left(98^{89}+1\right)\left(98^{88}+1\right)}\)
\(=\dfrac{98^{99}-98^{98}+98^{88}-98^{89}}{\left(98^{89}+1\right)\left(98^{88}+1\right)}=\dfrac{98^{98}\left(98-1\right)-98^{88}\left(98-1\right)}{\left(98^{89}+1\right)\left(98^{88}+1\right)}\)
\(=\dfrac{97.98^{98}-97.98^{88}}{\left(98^{89}+1\right)\left(98^{88}+1\right)}=\dfrac{97.98^{88}\left(98^{10}-1\right)}{\left(98^{89}+1\right)\left(98^{88}+1\right)}>0\)
\(\Rightarrow C>D\)
CÁCH 1
Ta có \(A=\frac{89}{99}=\frac{99-1}{99}=\frac{99}{99}-\frac{1}{99}=1-\frac{1}{99}\)
\(B=\frac{98.99+1}{98.99}=\frac{98.99}{98.99}+\frac{1}{98.99}\)
Vì \(\frac{1}{98.99}< \frac{1}{99}\Rightarrow1+\frac{1}{98.99}>1-\frac{1}{99}\Rightarrow\frac{98.99+1}{98.99}>\frac{98}{99}\Rightarrow B>A\)
CÁCH 2
Ta thấy 98 < 99 nên \(\frac{98}{99}< 1\)hay \(A< 1\)
Ta thấy \(98.99+1>98.99\Rightarrow\frac{98.99}{98.99+1}>1\Rightarrow B>1\)
Vì A < 1 ; B > 1 nên A < B
\(A=\frac{98}{99}< 1;\Rightarrow A< 1\)
\(B=\frac{98.99+1}{98.99}\)
Ta loại các số chia hết cho nhau thì được
\(B=\frac{1.1+1}{1.1}=1+1=2\)
\(2>1;\Rightarrow B>1;\Rightarrow B>A\)
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\(A=\frac{98^{99}+1}{98^{89}+1}>\frac{98^{99}+1+97}{98^{89}+1+97}=\frac{98^{99}+98}{98^{89}+98}=\frac{98\left(98^{98}+1\right)}{98\left(98^{88}+1\right)}=B\)
Vậy A>B