I made this graph for you- the red is the 80%, and the green is the leftover 20%.
<span>12(5y+4)
= 12(5y) + 12(4)
= 60y + 48
hope it helps</span>
£7200
In first year depreciates by 20%, that is it is worth 80% of it's original value
80% =
= 0.8
value after 1 year = 0.8 × £10000 = £8000
In the second year it depreciates by 10% of it's value, that is it is worth 90% of it's value at the end of the first year.
90% =
= 0.9
value after 2 years = 0.9 × £8000 = £7200
If you mean proof that the opposite sides of a parallelogram are equal, you draw a diagonal then prove that the 2 triangles formed are congruent.