Construction of Functions help

tegra97

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Sep 2, 2006
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Hello, I'm having some trouble with this problem any help would be great!

Let I be an interval of the real line, and let f be a real-value function with I is a subset of Dom(f). f is increasing on I iff for all x,y in I, if x<y, then f(x)<f(y). We say f is decreasing on I iff for all x,y in I, if x<y, then f(x)>f(y). Prove that

h is increasing on I, where h=f+g, and f and g are increasing on I.

This is what I have so far, since h,f, and g are increasing then h(x)<h(y), f(x)<f(y), and g(x)<g(y). So h(x)<h(y) = f(x)<f(y) + g(x)<g(y). This is where I'm stuck, can anybody give me some pointers? Thanks!!
 
If I have read you problem correctly you are given that each of f & g is increasing and h=f+g then you are to prove that h is increasing.

If x<y the f(x)<f(y) & g(x)<g(y) from the given.
Adding, f(x)+g(x)<f(y)+g(y). That implies that h(x)<h(y).
QED
 
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