Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

$y= 3x+5$; $x_0=-1$

I know the answer is $3$ but I don't know how to solve it. Can you please help me?

share|cite|improve this question
$\frac{dy}{dx}=3$, a constant. So its value does not depend on $x_0$. – André Nicolas Feb 28 '13 at 23:47
So, that's it? Thank you so much! – Joanna Feb 28 '13 at 23:52
You are welcome. Sometimes when a problem is too simple, it can be puzzling. You might have had an easier time with $y=x^3+5x$. – André Nicolas Feb 28 '13 at 23:59

$$ {dy \over dx} \equiv \lim_{h \to 0} {f(x+h)-f(x) \over h} \\ $$

Where $y = f(x)$.

$$ {dy \over dx} = \lim_{h \to 0} {3 x + 3 h + 5 - 3 x - 5 \over h} = 3 $$

share|cite|improve this answer
That is the formula that we have been using in class and I didn't understand it. However, you have made it so much clear! Thank you! – Joanna Feb 28 '13 at 23:59
@SeanHaugh Are you sure you mean $\equiv$, instead of $=$? – Jeel Shah Feb 28 '13 at 23:59
@gekkostate, I'm not Sean Haugh, but the $\equiv$ sign is also used for definitions or identities. – George V. Williams Mar 1 '13 at 0:07
@GeorgeV.Williams oh! I was not aware of that. Thank you for the clarification. – Jeel Shah Mar 1 '13 at 0:43

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.