## anonymous 4 years ago find an equation for the line with the points 3,-7 and -6,9 in the general form Ax+By=C

1. anonymous

help

2. Mertsj

Did you find the slope of the line?

3. anonymous

no

4. Mertsj

That would be the first step. Do you know how to find the slope?

5. anonymous

yeah

6. Mertsj

Ok. Do it and tell me what you get.

7. anonymous

-16/9

8. Mertsj

That's what I got.

9. Mertsj

Now pick one of the points. Which one do you choose?

10. anonymous

3,-7

11. Mertsj

$y-y _{1}=m(x-x _{1})$

12. Mertsj

Put -7 in place of y1. Put -16/9 in place of m and put 3 in place of x1

13. Mertsj

$y-(-7)=-\frac{16}{9}(x-3)$ $y+7=\frac{-16}{9}x+\frac{16}{3}$ $y=\frac{-16}{9}x-\frac{5}{3}$

14. Mertsj

Is that what you got?

15. anonymous

no, if you minus 7, u have to minus it from both sides

16. anonymous

that , and its not in the form Ax+By=C

17. Mertsj

Whoops. I forgot about that part. Let's rearrange it.

18. anonymous

the actual answer is 16x+9y=-15, but i dont know how to get there

19. Mertsj

$y=\frac{-16}{9}x-\frac{5}{3}$ Multiply both sides by 9 to clear the fractions

20. Mertsj

$9(y)=9(\frac{-16}{9})x-9(\frac{-5}{3})$

21. Mertsj

$9y=-16x+15$

22. Mertsj

Correction: 9y=-16x-15

23. Mertsj

16x+9y=-15

24. anonymous

how did you get 5-3?

25. anonymous

i mean 5/3

26. Mertsj

16/3-7

27. Mertsj

$y+7=\frac{-16}{9}x+\frac{16}{3}$

28. Mertsj

subtract 7 from both sides in that equation.

29. Mertsj

16/3-7=-5/3

30. anonymous

so u use point slope form to find b, then rearange to fit Ax+By=c?

31. Mertsj

yes. or you could use slope-intercept form if you prefer.

32. anonymous

how would slope intercept work

33. Mertsj

$y=mx+b$ $7=\frac{-16}{9}(3)+b$

34. Mertsj

Make the 7 negative.

35. Mertsj

$-7=\frac{-16}{3}+b$

36. Mertsj

37. Mertsj

$\frac{-5}{3}=b$

38. Mertsj

$y=\frac{-16}{9}x-\frac{5}{3}$

39. Mertsj

do you understand?

40. anonymous

awsome, thank you

41. Mertsj

yw. Now practice some more problems so you can fix it in your mind.