Question

Solve: |-7x| > 21

A. -3 < x < 3
B. -3 > x < 3
C. x > -3
D. x < -3 or x > 3

I think it's B, am I right?

Answer 1

Help! :D @zepdrix

Answer 2

I'm just confused because of the signs ._.

Answer 3

i think D is correct

Answer 4

because
\[/-7x/>21\]
\[-21>-7x >21\]
\[3<x <-3\]

Answer 5

Absolute algebra is |A.B|=|A|.|B|. So

|-7x| > 21 implies
|-1|.|7|.|x| >21 implies
1.7.|x|>21 implies
|x|>3

Which means X>3 or X<-3 i.e. D is the correct answer.

Answer 6

To make it more intuitive, in the attached graph of |x| against x (red) you can see that for |x| > 3 (bold red) then either x>3 or x <-3