Áp dụng liên tục a² - b² = (a - b)(a + b)   để biến đổi . Ta có: 

A = 3³² - 1 = (3¹⁶ - 1)(3¹⁶ + 1) = (3⁸- 1)(3⁸ + 1)(3¹⁶ + 1) = (3⁴ - 1)(3⁴ + 1)(3⁸ + 1)(3¹⁶ + 2) = (3² - 1)(3² + 1)(3⁴ + 1)(3⁸ + 1)(3¹⁶ + 1) =

    = (3 - 1)(3 + 1)(3² + 1)(3⁴ + 1)(3⁸ + 1)(3¹⁶ + 1) = 2.B 

Ta có 2B = \(\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

2B = (3⁴-1)(3⁴+1)(3⁸+1)(3¹⁶+1)

2B = (3⁸-1)(3⁸+1)(3¹⁶+1)

Tương tự ta đc: 

2B = 3³²-1

B= 3³²-1/2 hay B= A/2

Vậy A>B

ta có : B=(3+1)(3^2  +1)(3^4  +1)(3^8  +1)(3^16  +1)

=>(3-1)B=(3-1)(3+1)(3^2  +1)(3^4 +1)(3^8  +1)(3^16  +1)

=>2B=((3^2  -1)(3^2  +1)(3^4 +1)(3^8 +1)(3^16 +1)

=>2B=(3^4 -1)(3^4 +1)(3^8 +1)(3^16 +1)

=>2B=(3^8 -1)(3^8 +1)(3^16 +1)

=.2B=(3^16 -1)(3^16 +1)

=>2B=3^32  -1

=>B=(3^32  -1)/2, mà A=3^32  -1 nên  B=A/2 hay A=2B

\(B=\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(=\frac{1}{2}\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(=\frac{1}{2}\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

                \(.........\)

\(=\frac{1}{2}\left(3^{32}-1\right)\)\(< \)\(3^{32}-1\)\(=\)\(A\)

Vậy  \(B< A\)

 A=1.853020189*10 \(^{15}\)

B= 9.265100944*10\(^{15}\)

tự so sánh

Xét B ta có:

\(2B=2\left(3+1\right).\left(3^2+1\right).\left(3^4+1\right).\left(3^8+1\right).\left(3^{16}+1\right)\)

\(2B=\left(3-1\right)\left(3+1\right).\left(3^2+1\right).\left(3^4+1\right).\left(3^8+1\right).\left(3^{16}+1\right)\)

\(2B=\left(3^2-1\right).\left(3^2+1\right).\left(3^4+1\right).\left(3^8+1\right).\left(3^{16}+1\right)\)

\(2B=\left(3^4-1\right).\left(3^4+1\right).\left(3^8+1\right).\left(3^{16}+1\right)\)

\(2B=\left(3^8-1\right).\left(3^8+1\right).\left(3^{16}+1\right)\)

\(2B=\left(3^{16}-1\right).\left(3^{16}+1\right)\)

\(2B=3^{32}-1\)

\(B=\frac{3^{32}-1}{2}< A=3^{32}-1\)

Vậy B < A

Baì này mình mới làm lúc sáng bạn vào câu hỏi tương tự có đấy

\(A=\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^{16}-1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=3^{32}-1\)

\(\Rightarrow A=\frac{3^{32}-1}{2}< 3^{32}-1=C\)

Ta có: \(A=3^{32}-1=\left(3^{16}+1\right)\left(3^{16}-1\right)\)

\(=\left(3^{16}+1\right)\left(3^8+1\right)\left(3^8-1\right)\)

\(=\left(3^{16}+1\right)\left(3^8+1\right)\left(3^4+1\right)\left(3^4-1\right)\)

\(=\left(3^{16}+1\right)\left(3^8+1\right)\left(3^4+1\right)\left(3^2+1\right)\left(3^2-1\right)\)

\(=\left(3^{16}+1\right)\left(3^8+1\right)\left(3^4+1\right)\left(3^2+1\right)\left(3+1\right)\left(3-1\right)\)

\(=2.\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

Vậy A = 2B

\(a.\)

Ta sẽ biến đổi biểu thức  \(B\)  quy về dạng có thể dùng được hằng đẳng thức  \(\left(x-y\right)\left(x+y\right)=x^2-y^2\), khi đó:

\(B=\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)=\left(2-1\right)\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)

                                                                                     \(=\left(2^2-1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)

                                                                                     \(=\left(2^4-1\right)\left(2^4+1\right)\left(2^8+1\right)\)

                                                                                     \(=\left(2^8-1\right)\left(2^8+1\right)=2^{16}-1\)

Vì  \(2^{16}>2^{26}-1\)  nên  \(2^{16}>\left(2+1\right)\left(2^2+1\right)\left(2^4+1\right)\left(2^8+1\right)\)

Vậy,  \(A>B\)

Tương tự với câu  \(b\)  kết hợp với phương pháp tách hạng tử, khi đó xuất hiện hằng đẳng thức mới và dễ dàng đơn giản hóa biểu thức \(A\). Ta có:

\(A=4\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)=\frac{1}{2}\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)

                                                                                \(=\frac{1}{2}\left(3^4-1\right)\left(3^4+1\right)...\left(3^{64}+1\right)\)

                                                                                \(=\frac{1}{2}\left(3^{64}-1\right)\left(3^{64}+1\right)=\frac{1}{2}\left(3^{128}-1\right)\)

Mặt khác, do  \(\frac{1}{2}<1\)  nên   \(\frac{1}{2}\left(3^{128}-1\right)<3^{128}-1\)

Vậy,  \(B>A\)

Nếu đề thế này thì mình có thể làm được:

\(A=\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3-1\right)\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^8-1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=\left(3^{16}-1\right)\left(3^{16}+1\right)\)

\(\Rightarrow2A=3^{32}-1\)

\(\Rightarrow A=\dfrac{3^{32}-1}{2}\)

=> B>A

B>A

Ta có: B=\(\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

\(\Leftrightarrow\) 2B= \(2.\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

= \(\left(3-1\right).\left(3+1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

= \(\left(3^2-1\right)\left(3^2+1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

= \(\left(3^4-1\right)\left(3^4+1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

= \(\left(3^8-1\right)\left(3^8+1\right)\left(3^{16}+1\right)\)

= \(\left(3^{16}-1\right)\left(3^{16}+1\right)\)

= \(3^{32}-1\)

\(\Rightarrow\) B= \(\dfrac{3^{32}-1}{2}\)

Mà ta có A= \(3^{32}-1\)

\(\Rightarrow\) A=2B

a) \(\left(a-b+c\right)^2-\left(b-c\right)^2+2ab-2ac\)

\(=\left(a^2+\left(-b\right)^2+c^2-2ab+2ac-2bc\right)-\left(b^2-2bc+c^2\right)+2ab-2ac\)

\(=a^2+b^2+c^2-2ab+2ac-2bc-b^2+2bc-c^2+2ab-2ac\)

\(=a^2+b^2-b^2+c^2-c^2-2ab+2ab+2ac-2ac-2bc+2bc\)

\(=a^2\)