Question

Tìm x thuộc Q , biết

a) x² + 1 = 82

b) x² + 7/4 = 23/4

c) (2x+3)² = 25

Answer 1

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

=>x\(^2\) = 82 -1 = 81

=>x\(^2\) = 9\(^2\)

=>x =9 hoặc x = -9

Answer 2

b,x\(^2\) + \(\dfrac{7}{4}\) =\(\dfrac{23}{4}\)

=>x\(^2\) =\(\dfrac{23}{4}\) -\(\dfrac{7}{4}\)

=>x\(^2\) =\(\dfrac{16}{4}\) =4

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

=>x = 2

Answer 3

c,(2x+3)\(^2\) = 25

=>(2x+3)\(^2\) = 5\(^2\)

=>2x+3 = 5

=>2x = 5-3 =2

=>x = 2:2

=>x=1