# Thread: Definition of a derivative question

1. ## Definition of a derivative question

I know how to do this question when it comes to polynomials, but I dont know how to use them when it comes to square roots or trigonometry. I presume theres an identity when it comes to the trig part, but ive been trying for too long.

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2. Originally Posted by iPod
I know how to do this question when it comes to polynomials, but I dont know how to use them when it comes to square roots or trigonometry. I presume theres an identity when it comes to the trig part, but ive been trying for too long.

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Here you can find some good similar questions + answers to them.
Derivatives Using the Limit Definition

3. Originally Posted by iPod
I know how to do this question when it comes to polynomials, but I dont know how to use them when it comes to square roots or trigonometry. I presume theres an identity when it comes to the trig part, but ive been trying for too long.

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For example. $\frac{\sqrt{x+h}-\sqrt{x}}{h}=\frac{1}{\sqrt{x+h}+\sqrt{x}} \rightarrow \frac {1} {2 \sqrt{x}}$ , by multiplying both numerator and denominator

by the conjugate of the original numerator.

Tonio