Question

( - 2x ).( - 4x ) + 28 = 100

trình bày chi tiết cho mình nha

Answer 1

( -2x ) . ( -4x ) +28 = 100

( -2x ) . ( -4x ) = 100 - 28

( -2x ) . ( -4x ) = 72

8x² = 72

x² = 9

x = 3

Answer 2

\(\left(-2x\right).(- 4x) + 28 = 100\\ \Rightarrow\left(-2\right).x.\left(-4\right).x=100-28\\ \Rightarrow8.x^2=72\\ \Rightarrow x^2=72:8\\ \Rightarrow x^2=9\\ \Rightarrow x^2=3^2=\left(-3\right)^2\\ \Rightarrow x\in\left\{3;-3\right\}\)

Vậy \(x\in\left\{3;-3\right\}\)

Thấy đúng cho tớ 1 tick nhé cậu