\(A=5a^3b^4-9a^{11}b^2=a^3b^2\cdot5b^2-a^3b^2\cdot9a^8=a^3b^2\left(5b^2-9a^8\right)\)

Thay \(a=-1\) và \(b=2\) vào biểu thức A, ta có:

\(A=\left(-1\right)^3\cdot2^2\left(5\cdot2^2-9\left(-1\right)^8\right)=-1\cdot4\left(5\cdot4-9\cdot1\right)=-4\left(20-9\right)=-4\cdot11=-44\)

Có vẻ như đề bài biểu thức B không đúng vậy. Sửa \(by\) ở cuối thành \(ay\).

\(B=ax+by+bx+ay=\left(ax+ay\right)+\left(bx+by\right)=a\left(x+y\right)+b\left(x+y\right)=\left(a+b\right)\left(x+y\right)\)

Thay \(a+b=-2\) và \(x+y=17\) vào biểu thức B, ta có:

\(B=-2\cdot17=-34\)

b: Xét ΔABH vuông tại H có 

\(AB^2=AH^2+HB^2\)

hay AH=12(cm)

Xét ΔAHB vuông tại H có 

\(\sin\widehat{B}=\cos\widehat{C}=\dfrac{AH}{AB}=\dfrac{12}{13}\)

\(\cos\widehat{B}=\sin\widehat{C}=\dfrac{5}{13}\)

\(\tan\widehat{B}=\cot\widehat{C}=\dfrac{12}{5}\)

\(\cot\widehat{B}=\tan\widehat{C}=\dfrac{5}{12}\)

(a,b)=45 là UCLN(a,b)=45 đúng ko

a; a - b ⋮ 6

    a - b + 12b ⋮ 6

   a + 11b ⋮ 6 (đpcm)

b;  a - b ⋮ 6

     a -  b  - 12a ⋮ 6

          -11a - b ⋮ 6

        -(11a + b) ⋮ 6

         11a + b    ⋮ 6 (đpcm)

Em cảm ơn cô ạ

2 she had got the price of the contest, she would be happy now

3 I had gone to the concert last night ,I would be tired

4 John had finished all his homework, he could see a movie now

5 we had listened to my mother, we wouldn't be in trouble right now

Ex5

1 you arrive at the offcie earlier than I do, please turn on the air-conditioner

2 Were it not snowy, the children would go to school

3 he not died so young, he would be a famous musician

4 Were I you, I would take care of my car

5 not very bad-tempered, his wife would give him soon are marrage

6 Had she not got married at such an early age, he would be at university

a. x² - 11 = \(x^2-\left(\sqrt{11}\right)^2=\left(x-\sqrt{11}\right)\left(x+\sqrt{11}\right)\)

b. x² - 5 = \(x^2-\left(\sqrt{5}\right)^2=\left(x-\sqrt{5}\right)\left(x+\sqrt{5}\right)\)

c. x² - 7 = \(x^2-\left(\sqrt{7}\right)^2=\left(x+\sqrt{7}\right)\left(x-\sqrt{7}\right)\)

Câu 3: Kết quả nào sau đây là của biểu thức Sum(6) - max(5)

A. 11
B. 1
C. -1
D. Tất cả sai

B