a) Ta có :

\(AB^2=3^2=9\left(cm\right)\)

\(AC^2=4^2=16\left(cm\right)\)

\(BC^2=5^2=25\left(cm\right)\)

=> \(BC^2=AB^2+AC^2\)

=> \(5^2=3^2+4^2\) (cm)

=> \(25=9+14\) (cm)

<=> \(\Delta ABC\perp A\)

b) Xem lại đề

Mark the letter A, B, C or D on your answer sheet to indicate the word that differs from the three in the position of primary stress in each of the following questions.

A. doctor

B. birthday

C. concert

D. address

\(\left|2\text{x}-3\right|-x=\left|2-x\right|\)

=> \(2\text{x}-3-x=2-x\) hoặc \(2\text{x}-3-x=-2+x\)

TH1 :

\(2\text{x}-3-x=2-x\)

=> 2x - 3 - x - 2 + x=0

=> 2x - 3 -2 = 0

=> 2x - 5 =0

=> 2x = 5

=> x = \(\dfrac{5}{2}\)

TH2 :

\(2\text{x}-3-x=-2+x\)

=> \(2\text{x}-3-x+2-x\) = 0

=> 0x -3 + 2 = 0

=> 0x - 1 = 0

=> 0x = 1 ( Không có x )

Vậy : x = \(\dfrac{5}{2}\)