so sánh A=1+1:2+1:3+...+1:64 và B=4
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A= 80.(34 + 1)(38 + 1)(316 + 1)(332 + 1)
A = (34 - 1)(34 + 1)(38 + 1)(316 + 1)(332 + 1)
A = (38 - 1)(38 + 1)(316 + 1)(332 + 1)
A = (316 - 1)(316 + 1)(332 + 1)
A = (332 - 1)(332 + 1)
A = 364 - 1 < 364 = B
=> A < B
a: \(A=1999\cdot2001\)
\(=\left(2000-1\right)\left(2000+1\right)\)
\(=2000^2-1=B-1\)
=>A<B
b: \(B=\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)
\(=\left(2-1\right)\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)
\(=\left(2^2-1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)
\(=\left(2^4-1\right)\left(2^4+1\right)\left(2^8+1\right)\)
\(=\left(2^8-1\right)\left(2^8+1\right)=2^{16}-1\)
=A-1
=>B<A
c: \(A=2011\cdot2013\)
\(=\left(2012-1\right)\left(2012+1\right)=2012^2-1\)
=B-1
=>A<B
d: \(A=4\left(3^2+1\right)\left(3^4+1\right)\cdot\ldots\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\cdot\ldots\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\cdot\ldots\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^8-1\right)\left(3^8+1\right)\left(3^{16}+1\right)\cdot\left(3^{32}+1\right)\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^{16}-1\right)\left(3^{16}+1\right)\cdot\left(3^{32}+1\right)\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^{32}-1\right)\cdot\left(3^{32}+1\right)\cdot\left(3^{64}+1\right)\)
\(=\frac12\left(3^{64}-1\right)\cdot\left(3^{64}+1\right)=\frac12\left(3^{128}-1\right)\)
=1/2B
=>A<B