Rút gọn biểu thức:
A = (3 + 1) (32 + 1) (34 + 1) ... (364 + 1)
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\(\left(3-1\right)A=\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\\ 2A=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\\ 2A=\left(3^4-1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\\ 2A=\left(3^8-1\right)\left(3^8+1\right)...\left(3^{64}-1\right)\\ ...\\ 2A=\left(3^{64}-1\right)\left(3^{64}+1\right)\\ 2A=3^{128}-1\)
Vậy \(A=\dfrac{3^{128}-1}{2}.\)
a.Chứng tỏ rằng B = 1/22 + 1/32 + 1/42 + 1/52 + 1/62 + 1/72 +1/82 < 1
b.Cho S = 3/1.4 + 3/4.7 + 3/7.10 +......+3/40.43 + 3/43.46 hãy chứng tỏ rằng S < 1
Xin lỗi mọi người mình tính đặt câu hỏi nhưng ấn nhầm phần trả lời ạ!
`A=1/[\sqrt{3}+1]+1/[\sqrt{3}-1]`
`A=[\sqrt{3}-1+\sqrt{3}+1]/[3-1]`
`A=[2\sqrt{3}]/2=\sqrt{3}`
\(A=\dfrac{1}{\sqrt{3+1}}+\dfrac{1}{\sqrt{3-1}}\)
\(A=\dfrac{\sqrt{3-1+\sqrt{3+1}}}{\left(\sqrt{3+1}\right)\left(\sqrt{3-1}\right)}\)
\(A=\dfrac{2\sqrt{3}}{3-1}\)
\(A=\dfrac{2\sqrt{3}}{2}\)
\(A\sqrt{3}\)
Ta có :
\(A=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{2012}}\)
\(2A=1+2+\frac{1}{2}+...+\frac{1}{2^{2011}}\)
\(2A-A=\left(1+2+\frac{1}{2}+...+\frac{1}{2^{2011}}\right)-\left(1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{2012}}\right)\)
\(A=2-\frac{1}{2^{2012}}\)
\(A=\frac{2^{2013}-1}{2^{2012}}\)
Vậy \(A=\frac{2^{2013}-1}{2^{2012}}\)
\(A=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{2012}}\)
=>2A=\(2+1+\frac{1}{2}+...+\frac{1}{2^{2011}}\)
=>2A-A=\(\left(2+1+\frac{1}{2}+...+\frac{1}{2^{2011}}\right)-\left(1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{2012}}\right)=2-\frac{1}{2^{2012}}\)
=>A=\(\frac{2^{2013}-1}{2^{2012}}\)