It is known that f (x) is a decreasing function on a set of real numbers. If a + B ≤ 0, then the following is true? A.f（a）+f（b）≤-{f（a）+f（b）} B.f（a）+f（b）≤f(-a)+f(-b） c.f(a）+f（b）≥-｛f（a）+f（b）｝ d.f（a）+f（b）≥f（-a）+f（-b） 2. Given that f (x) is an odd function, if x > 0, f (x) = X-1, then f (x)

It is known that f (x) is a decreasing function on a set of real numbers. If a + B ≤ 0, then the following is true? A.f（a）+f（b）≤-{f（a）+f（b）} B.f（a）+f（b）≤f(-a)+f(-b） c.f(a）+f（b）≥-｛f（a）+f（b）｝ d.f（a）+f（b）≥f（-a）+f（-b） 2. Given that f (x) is an odd function, if x > 0, f (x) = X-1, then f (x)

1
From a + B ≤ 0
Then a ≤ - B, B ≤ - A
So there is
f(a)≥f(-b),
f(b)≥f(-a)
Add two formulas and choose D
2 Ling x 0
f(-x)=-x-1
If f (x) is an odd function, then
f(x)=-f(-x)=x+1
[this is x0
Inequality can be reduced to
x-1

Let f (x) be a decreasing function on a set of real numbers. If a + B ≤ 0, then the following is true ()
A. f（a）+f（b）≤-[f（a）+f（b）]B. f（a）+f（b）≤f（-a）+f（-b）C. f（a）+f（b）≥f（-a）+f（-b）D. f（a）+f（b）≥-[f（a）+f（b）]

∵ a + B ≤ 0, ∵ a ≤ - B, B ≤ - A, ∵ f (x) is a decreasing function on the set of real numbers, ∵ f (a) ≥ f (- b), f (b) ≥ f (- a). By adding the two formulas, f (a) + F (b) ≥ f (- a) + F (- b) is obtained

F (x) is a decreasing function on a set of real numbers if a + B is less than or equal to 0,
A f (a) + F (b) is greater than or equal to - [f (a) + F (b)]
B F (a) + F (b) less than or equal to - [f (a) + F (b)]
Which do you choose?
Some of my classmates choose a, some choose B, and a good student says AB can't get

If the image is above the x-axis, select a;
If the image is below the x-axis, select B;
If the intersection, you need to see the location of the intersection, so, this problem points discussion