## j2lie one year ago If the slope of the line that passes through the points (a,0) and (1,-2) is 1/2, what is the value of a? @jim_thompson5910

1. freckles

have you applied the slope formula?

2. freckles

$m=\frac{y_2-y_1}{x_2-x_1}$

3. j2lie

No. I do not know that to do that with this problem.

4. freckles

well you are given two points on a line and the slope ... which makes me think slope formula since only one of the values is unknown in the pairs given you are given m is 1/2 (x1,y1)=(1,-2) and (x2,y2)=(a,0)

5. freckles

$\frac{1}{2}=\frac{0-(-2)}{a-1}$ solve for a

6. j2lie

a = -2

7. freckles

how did you get that?

8. j2lie

0 + 2 is 2 and a - 1 is -1

9. freckles

it might make it easier on you if you flip both sides $\frac{2}{1}=\frac{a-1}{0-(-2)}$ see if you can solve now

10. freckles

by the way 2/1 is just 2

11. jdoe0001

$$\bf \begin{array}{lllll} &x_1&y_1&x_2&y_2\\ % (a,b) &({\color{red}{ a}}\quad ,&{\color{blue}{ 0}})\quad % (c,d) &({\color{red}{ 1}}\quad ,&{\color{blue}{ -2}}) \end{array} \\\quad \\ % slope = m slope = {\color{green}{ m}}= \cfrac{rise}{run} \implies \cfrac{{\color{blue}{ y_2}}-{\color{blue}{ y_1}}}{{\color{red}{ x_2}}-{\color{red}{ x_1}}}\implies \cfrac{{\color{blue}{ -2}}-{\color{blue}{ 0}}}{{\color{red}{ 1}}-{\color{red}{ a}}}=\cfrac{1}{2}$$

12. j2lie

I am confused now.

13. freckles

confused on how to solve 2=(a-1)/2 for a?

14. j2lie

Yes.

15. freckles

are confused on the flipping part? confused on the equation we got?

16. j2lie

I am confused on solving with A.

17. freckles

solving with A?

18. freckles

what does that mean

19. freckles

you mean solve for a?

20. j2lie

The variable is A in the equation

21. freckles

don't we have a not A? $\frac{1}{2}=\frac{0-(-2)}{a-1} \\ \\ 0-(-2) \text{ is the same as } 2 \\ \text{ you have } \\ \frac{1}{2}=\frac{2}{a-1}$

22. freckles

you can flip both sides like I did earlier $\frac{2}{1}=\frac{a-1}{2} \\ \text{ now } \frac{2}{1}=2 \\ 2=\frac{a-1}{2}$

23. freckles

try to undo that division by 2 ...multiply 2 on both sides

24. j2lie

1=4/a-1?

25. freckles

well 2 times 2 is 4 not 1 and how did you put a-1 back in the denominator? also 2/2=1 not 4...

26. freckles

oh you went backwards

27. j2lie

it is 1/2 times 2

28. freckles

do you see this equation 2=(a-1)/2 I was asking you multiply this equation by 2 on both sides

29. freckles

this gives you 4=a-1

30. j2lie

how did you get 2?

31. freckles

@Jhannybean you can finish i have to leave I'm sorry

32. j2lie

I get it now.

33. Jhannybean

$2=\frac{a-1}{2} \implies 4 = a-1 \implies a= 4+1$

34. j2lie

That is what I got.

35. j2lie

Thank you.