Original post by izzy21234
Hey this is probably quite a simple question but i just cant get around it!
"h(x) = x^3+qx. find the range of values of q for which h(x) is increasing for all real values of x."
i got to q is greater than -3x^2 but apparently the answer is 0. how do i get there?
"h(x) = x^3+qx. find the range of values of q for which h(x) is increasing for all real values of x."
i got to q is greater than -3x^2 but apparently the answer is 0. how do i get there?
Assuming your working starts with "h(x) > 0", that's not what "increasing" means.
For instance, 1/x > 0 for all positive x, but clearly it is not increasing in that domain.
See mqb's comment for hint.
Something minor to note, we say a function is increasing if x > y implies f(x) >= f(y). The equality is there.
So a function like y=0 is increasing by definition, despite what English tells you.
That said, is the "definition" way the best method to tackle this problem? Probably not.
(edited 10 months ago)
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