What is the mathematical expression for a function to be strictly decreasing on (a,b)?

• A. x1 = x2 ⇒ f(x1) ≤ f(x2) ∀ x1, x2 ∈ (a,b)b) x1 < x2 ⇒ f(x1) > f(x2) ∀ x1, x2 ∈ (a,b)c) x1 < x2 ⇒ f(x1) < f(x2) ∀ x1, x2 ∈ (a,b)d) x1 < x2 ⇒ f(x1) = f(x2) ∀ x1, x2 ∈ (a,
• B. ?a) x1 = x2 ⇒ f(x1) ≤ f(x2) ∀ x1, x2 ∈ (a,b)b) x1 < x2 ⇒ f(x1) > f(x2) ∀ x1, x2 ∈ (a,b)
• C. x1 < x2 ⇒ f(x1) < f(x2) ∀ x1, x2 ∈ (a,b)
• D. x1 < x2 ⇒ f(x1) = f(x2) ∀ x1, x2 ∈ (a,b)