can someone explain this?

[santasad13]

([=absolute value)
[7-x]=10 x=-3 or x=17

as you can tell, i suck at math.

also,a + 2b = 1 and 3a - 8b = 1
The price of a sweater went up 20% since last year. If last year’s price was x, what is this year’s price in terms of x?

thanks

 

[pka]

One can type |x| by ‘shift \’.

The absolute value of a number is its distance from zero.
To say |7−x|=10 is to say (7−x) is a number 10 units from 0
10 is ten units from 0; −10 is also ten units from 0.
Thus we get 7−x=10 or 7−x=−10.