Bài 1:

A = 8.(3² + 1)(3⁴ + 1)(3⁸ + 1)(3¹⁶ + 1)

A = (3^{2 -} 1)(3² + 1)(3⁴+ 1)(3⁸ +1)(3¹⁶ + 1)

A = (3⁴ - 1)(3⁴ + 1)(3⁸+ 1)(3¹⁶ + 1)

A = (3⁸ - 1)(3⁸ + 1)(3¹⁶ + 1)

A = (3¹⁶ - 1)(3¹⁶ +1)

 A = (3¹⁶)² - 1²  

A = 3³² - 1

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

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

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

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

\(=\left(3^{16}-1\right)\left(3^{16}+1\right)=3^{32}-1\)

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

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

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

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

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

3: \(C=24\left(5^2+1\right)\left(5^4+1\right)\cdot...\cdot\left(5^{128}+1\right)+\left(5^{256}-1\right)\)

\(=\left(5^2-1\right)\left(5^2+1\right)\cdot\left(5^4+1\right)\left(5^{128}+1\right)+\left(5^{256}-1\right)\)

\(=\left(5^4-1\right)\cdot\left(5^4+1\right)\cdot...\cdot\left(5^{128}+1\right)+\left(5^{256}-1\right)\)

\(=\left(5^8-1\right)\left(5^8+1\right)\cdot...\cdot\left(5^{128}+1\right)+\left(5^{256}-1\right)\)

\(=\left(5^{16}-1\right)\left(5^{16}+1\right)\cdot...\cdot\left(5^{128}+1\right)+5^{256}-1\)

\(=\left(5^{32}-1\right)\left(5^{32}+1\right)\left(5^{64}+1\right)\left(5^{128}+1\right)+5^{256}-1\)

\(=\left(5^{64}-1\right)\left(5^{64}+1\right)\left(5^{128}+1\right)+5^{256}-1\)

\(=\left(5^{128}-1\right)\left(5^{128}+1\right)+5^{256}-1=2\left(5^{256}-1\right)\)

\(10x-x^2+2\\ =\left(-x^2+10x-25\right)+27\\ =-\left(x^2-10x+25\right)+27\\ =-\left(x-5\right)^2+27\)
Ta có: \(-\left(x-5\right)^2\le0\forall x=>-\left(x-5\right)^2+27\le27\forall x\)

Dấu "=" xảy ra: `x-5=0<=>x=5` 

1) 12 ⋮ x => x ∈ Ư(12) = {1; -1; 2; -2; 3; -3; 4; -4; 6; -6; 12; -12} 

Mà: x > 2 

=> x ∈ {3; 4; 6; 12} 

2) 24 ⋮ x => x ∈ Ư(24) = {1; -1; 2; -2; 3; -3; 4; -4; 6; -6; 8; -8; 12; -12; 24; -24} 

Mà: x > 4 

=> x ∈ {6; 8; 12; 24} 

3) 36 ⋮ x => x ∈ Ư(36) = {1; -1; 2; -2; 3; -3; 4; -4; 6; -6; 9; -9; 12; -12; 18; -18; 36; -36}

Mà: x ≥ 3 

=> x ∈ {3; 4; 6; 9; 12; 18; 36} 

4) 40 ⋮ x => x ∈ Ư(40) = {1; -1; 2; -2; 4; -4; 5; -5; 8; -8; 10; -10; 20; -20; 40; -40} 

Mà: x < 10 và x là số tự nhiên

=> x ∈ {1; 2; 4; 8}

Ta có:

\(Q=\dfrac{1}{x^2-4x+11}=\dfrac{1}{\left(x^2-4x+4\right)+7}\\ =\dfrac{1}{\left(x-2\cdot x\cdot2+2^2\right)+7}=\dfrac{1}{\left(x-2\right)^2+7}\) 

\(\left(x-2\right)^2\ge0\forall x=>\left(x-2\right)^2+7\ge7\forall x\\ =>Q=\dfrac{1}{\left(x-2\right)^2+7}\le\dfrac{1}{7}\forall x\)

Dấu "=" xảy ra: `x-2=0<=>x=2` 

Số sách đủ để chia là:

\(3+3=6\left(quyển\right)\)

Tổ được chia 8  quyển nhiều hơn tổ được chia 7 quyển là:

\(8-7=1\left(quyển\right)\)

Số tổ được chia sách là:

\(6:1=6\left(tổ\right)\)

Số sách văn và toán là:

ABCD là hình chữ nhật 

=> CD = AB = 4 (cm) 

=> AD = BC = 3 (cm) 

=> BD = AC = 5 (cm)

\(x^2+2>=2\forall x\)

=>\(\left(x^2+2\right)^2>=4\forall x\)

=>\(-\left(x^2+2\right)^2< =-4\forall x\)

mà \(-\left(y^2-16\right)^4< =0\forall y\)

nên \(-\left(x^2+2\right)^2-\left(y^2-16\right)^4< =-4\forall x,y\)

=>\(B=-\left(x^2+2\right)^2-\left(y^2-16\right)^4+20< =-4+20=16\forall x,y\)

Dấu '=' xảy ra khi \(\left\{{}\begin{matrix}x=0\\y^2-16=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0\\y\in\left\{4;-4\right\}\end{matrix}\right.\)

\(8-x>\dfrac{11}{3}\)

=>\(-x>\dfrac{11}{3}-8=-\dfrac{13}{3}\)

=>\(x< \dfrac{13}{3}\)

mà x là số tự nhiên lớn nhất có thể

nên x=4

            8 - \(x\) > \(\dfrac{11}{3}\)

 suy ra 8 - \(\dfrac{11}{3}\) > \(x\) 

           \(\dfrac{24}{3}\) - \(\dfrac{11}{3}\) > \(x\)

            \(\dfrac{13}{3}\) > \(x\)

           4\(\dfrac{1}{3}\) > \(x\)

Vậy \(x\) = 0; 1; 2; 3; 4

Vì \(x\) là số tự nhiên lớn nhất nên \(x\) = 4

Diện tích tam giác BAC là:

\(S_{BAC}=\dfrac{1}{2}\cdot BA\cdot BC\cdot sinABC=\dfrac{1}{2}\cdot5,2\cdot3,5\cdot sin75=\dfrac{91\sqrt{6}+91\sqrt{2}}{40}\)

ABCD là hình bình hành

=>\(S_{ABCD}=2\cdot S_{BAC}=\dfrac{91\sqrt{6}+91\sqrt{2}}{20}\)