## mitchelsewbaran 3 years ago If the 2 lines given by the equations 12x+3y=20 and ax+y=10 don't intersect when graphed, what is the value of "a"?

1. sasogeek

if they don't intersect, it means they're parallel and their gradient is the same. find the gradient of the first equation and that's equal to "a" :)

2. zzr0ck3r

set both equal to y, and make them have the same slope

3. zzr0ck3r

as long as they dont have the same y intercept they will not cross if they have the same slope

4. zzr0ck3r

3y = 20 -3x y = -x-(20/3) and the other equation set to y is what?

5. zzr0ck3r

@mitchelsewbaran ?

6. mitchelsewbaran

hmmm.....

7. zzr0ck3r

that should be +(20/3)

8. zzr0ck3r

y = -x+(20/3)

9. zzr0ck3r

solve for y in the second equation

10. zzr0ck3r

y = -ax+10 we want them to have the same slope so what does a need to be? y = -x+(20/3) y = -ax+10 a = ?

11. mitchelsewbaran

10?

12. sasogeek

12x+3y=20 solve for y 3y=-12x+20 y=-4x+(20/3) can u tell what the slope is?

13. sasogeek

@mitchelsewbaran ... ?

14. mitchelsewbaran

hold on