An = 3.5 +2.8 (n-1)
f(n) =

f(n) = 2.8n + 0.7

Step-by-step explanation:

The form of the linear function is f(x) = m x + b, where

Let us solve the question

∵ The rule of the arithmetic sequence is a = 3.5 + 2.8(n - 1), where

→ To write it as a function replace a by f(n)

∵ a = f(n)

∴ f(n) = 3.5 + 2.8(n - 1)

→ Simplify the right side to make it in the form of the function above

∵ f(n) = 3.5 + 2.8(n) + 2.8(-1)

→ Remember (+)(-) = (-)

∴ f(n) = 3.5 + 2.8n - 2.8

→ Add the like terms in the right side

∵ f(n) = 2.8n + (3.5 - 2.8)

∴ f(n) = 2.8n + 0.7

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.