Question

Bài 12: Tìm x ϵ Q, biết:

a. x² + 1 = 82

b. x² + 7/4 = 23/4

c. (2x+3)² = 25

Answer 1

a. x² + 1 = 82

=> x² = 81

=> x² = 9²

=> x = 9 hoặc x = - 9

b. x² + 7/4 = 23/4

=> x² = 4

=> x² = 2²

=> x = 2 hoặc x = - 2

c. ( 2x + 3 )² = 25

=> ( 2x + 3 )² = 5²

=>  2x + 3 = 5 hoặc  2x + 3 = - 5

=> x = 1 hoặc x = - 4

Answer 2

a, \(x^2+1=82\Leftrightarrow x^2=81\Leftrightarrow x=\pm9\)

b, \(x^2+\frac{7}{4}=\frac{23}{4}\Leftrightarrow x^2=4\Leftrightarrow x=\pm2\)

c, \(\left(2x+3\right)^2=25\Leftrightarrow2x+3=\pm5\Leftrightarrow\orbr{\begin{cases}2x+3=5\\2x+3=-5\end{cases}\Leftrightarrow\orbr{\begin{cases}x=4\\x=-1\end{cases}}}\)

Answer 3

a) x² + 1 = 82

<=> x² = 81

<=> x² = ( ±9 )²

<=> x = ±9

b) x² + 7/4 = 23/4

<=> x² = 4

<=> x² = ( ±2 )²

<=> x = ±2

c) ( 2x + 3 )² = 25

<=> ( 2x + 3 )² = ( ±5 )²

<=> 2x + 3 = 5 hoặc 2x + 3 = -5

<=> x = 1 hoặc x = -4

Answer 4

bằng-4