I'm trying to solve this question using the definition of integral:
$$\int^5_2 (4-2x)dx$$
Definition of integral:
We define first the inferior and superior sum:
Let $f:[a,b]\to \mathbb R$ be a bounded function and $P=\{t_0,\ldots,t_n\}$ a partition of [a,b], so we define:
$$s(f;P)=\sum_{i=1}^nm_i(t_i-t_{i-1})$$
$$S(f;P)=\sum_{i=1}^nM_i(t_i-t_{i-1})$$
Where $m_i=\inf\{f(x);x\in [t_i,t_{i-1}]\}$ and $M_i=\sup\{f(x);x\in [t_i,t_{i-1}]\}$ and ().
No we define the inferior and superior integral:
Inferior integral: $\underline\int^b_a=\sup_P s(f;P)$
Superior integral: $\bar\int^b_a=\inf_P s(f;P)$
At last, we define the integral being the superior or inferior integral when they are the same.
My attempt
I know:
$s(f,P)=\sum_{i=1}^n(4-2t_i)(t_i-t_{i-1})$ (because the function is decreasing)
But I don't know how to take the supreme of this sum.
Thanks.