Answer:
f(5) = 35
Explanation:
In any function f(x), x is the input and f(x) is the output
Example:
f(x) = 2x + 3, find f(a)
That means we need to find value of f(x) at x = a, so substitute x by a
f(a) = 2(a) + 3 = 2a + 3
f(a) = 2a + 3
Let us use the same way to solve our question
∵ f(x) = x² + 2x
→ We need to find f(5), so substitute x by 5
∴ f(5) = (5)² + 2(5)
∴ f(5) = 25 + 10
→ Do addition
∴ f(5) = 35