## znimon Group Title How do I find the domain of this function? one year ago one year ago

1. znimon Group Title

$g(x) \sqrt{x^2 - 3x - 40}$

2. znimon Group Title

I have $\sqrt{(x-8)(x+5)}$

3. znimon Group Title

$(x-8)(x+5) \ge 0$

4. znimon Group Title

The original problem is at the top.

5. Yahoo! Group Title

Draw a number line and see for it

6. znimon Group Title

I don't know what x can't be though

7. znimon Group Title

I know the answer but I don't know how to get the answer.

8. Yahoo! Group Title

(-infinity , 5] U [8 , infinity)

9. znimon Group Title

yeah but how do I find that?

10. Yahoo! Group Title

just do trial and error method...)

11. Yahoo! Group Title

(x−8)(x+5)≥0

12. Yahoo! Group Title

luk for the vlue of x which satisfies this...

13. znimon Group Title

There must be a logical way to find the answer, right?

14. ganeshie8 Group Title

(x-8)(x+5) >= 0 its a parabola, right ?

15. znimon Group Title

I could input it into my graphing calculator but other wise I don't know how to tell if its a parabola or not.

16. ganeshie8 Group Title

y = ax^2 + bx + c is a parabola

17. ganeshie8 Group Title

any quadratic function gives a parabola graph

18. znimon Group Title

ok

19. ganeshie8 Group Title

can you find the x intercepts ?

20. ganeshie8 Group Title

once you find x-intercepts, you would know where the parabola dips into x axis (goes negative)

21. ganeshie8 Group Title

|dw:1346519548989:dw|

22. znimon Group Title

Oh ya that would be the point at which the g(x) function is 0, so its x - 8 = 0, x = 8, x+ 5 = 0, x=-5, and since its a parabola the graph only passes through zero twice. Nice dude, so the domain is (-infinity, -5] U [8, +infinity]

23. ganeshie8 Group Title

yeah nice you got it :)

24. znimon Group Title

@ganeshie8

25. znimon Group Title

Awesome, thanks again. Is there a way I could recognize any graph's shape or at least some and would you recommend memorizing those?

26. ganeshie8 Group Title

if the degree is 2, then its a parabola

27. ganeshie8 Group Title

finding domains for other polynomials is bit tricky... as they may dip into x-axis multiple times

28. znimon Group Title

okay

29. ganeshie8 Group Title

do you knw sketching polynomilas (end behiavior thingy )

30. znimon Group Title

never heard of it

31. ganeshie8 Group Title

end behavior helps you sketch ANY polynomial freehand

32. znimon Group Title

Thanks dude, I'll look it up

33. ganeshie8 Group Title

process is basically : 1) find x intercepts 2) using end-behavior sketch the graph by hand

34. ganeshie8 Group Title

its easy concept and worth learning... im sure you wil get hang of it in few minutes....... good luck :)

35. znimon Group Title

why is it that a polynomial with a degree of two is a parabola?

36. znimon Group Title

Thanks again.

37. ganeshie8 Group Title

uhh il have to think...... idk exactly... i think it has something to do with local maximum/minimum + increasing/decreasing thingy. we need to turn to calculus for proper understanding. im also learning... . so im no good for answering this :(

38. ganeshie8 Group Title

@mukushla @eliassaab @experimentX

39. znimon Group Title

Oh, I have enough to learn for now so it doesn't matter to me. I bet I wouldn't understand the explanation if it involves terms I've never had before haha.