Question

Tìm x ( sử dụng các hằng đẳng thức )

a, 2x ( 2x + 5 ) - 4x ( x - 3 ) = 7

b, ( x + 2 ) ( x - 2 ) - ( x + 1 )\(^2\) = 2

c, ( x + 2 ) ( x - 1 ) - ( x + 3 ) ( x - 2 ) = 0

d, x\(^2\) - ( x - 1 )\(^2\) = 4

e, ( 2x + 3 ) ( 2x - 3 ) - ( 2x - 1 )\(^2\) = 6

f, ( x - 1 )\(^2\) - 25 = 0

Answer 1

a) \(2x\left(2x+5\right)-4x\left(x-3\right)=7\)

\(4x^2+10x-4x^2+12x=7\)

\(22x=7\Rightarrow x=0,31\)

b) \(\left(x+2\right)\left(x-2\right)-\left(x+1\right)^2=2\)

\(\left(x^2-4\right)-\left(x^2+2x+1\right)=2\)

\(x^2-4-x^2-2x-1=2\)

\(-2x=7\Rightarrow x=-3,5\)

c) \(\left(x+2\right)\left(x-1\right)-\left(x+3\right)\left(x-2\right)=0\)

\(x^2-x+2x-2-x^2+2x+3x-6=0\)

\(6x=8\Rightarrow x=1,3\)