Question 186634
Let {{{y}}} = the original value of the TV
given:
{{{120}}} = depreciation/1 year
You have to understand that depreciation
is what the TV loses in value each year,
so every year it's worth less, and then it
gets depreciated again
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{{{y - 120}}} is the value of the TV after 1 year
{{{y - 120 - 120}}} is the value of the TV after 2 years
{{{y - 120 - 120 - 120}}} is the value of the TV after 3 years
{{{y - 4*120}}} is the value of the TV after 4 years
The problem says the TV is worth $340 after 4 years, so
{{{y - 4*120 = 340}}}
{{{y = 340 + 480}}}
{{{y = 820}}}
So, the TV was originally worth $820
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Now I need to write a function that tells me the
value of the TV for any given year
If {{{x}}} is the year after purchase,
and {{{V(x)}}} is the value of the TV that year
{{{V(x) = 820 - 120x}}}
A quick check is:
What is the TV worth after 4 years?
{{{V(x) = 820 - 120x}}}
{{{V(4) = 820 - 480}}}
{{{V(4) = 340}}} 
That's what it should be