calculusxy one year ago Solving Systems of Equations by Substitution. 1. -3x + 3y = 4 -x + y = 3 2. -5x - 8y = 17 2x - 7y = -17

1. calculusxy

@jim_thompson5910 @Nnesha

2. calculusxy

@mathstudent55

3. calculusxy

This is my work for question 1. we could figure out the value of y by: y = 3 + x -3x + 3(3 + x) = 4 is that correct?

4. calculusxy

i need to solve for x, which i know, but i just wanted to know whether my set up was fine or not.

5. Nnesha

yep yep right :=)

6. calculusxy

so then we can simply it to: -3x + 9 + 3x = 4

7. Nnesha

yep

8. calculusxy

but if we do -3x + 3x = 0x and I am not even sure if there is any such thing as 0x.

9. Nnesha

yes so they cancel out

10. Nnesha

thats mean no solution both sides are not equal $9 \cancel =4$

11. calculusxy

oh okay :)

12. calculusxy

and for the next one...

13. Nnesha

yep

14. calculusxy

we can figure out the value of x... 2x - 7y = -17 2x = -17 + 7y 2x / 2 = (-17 + 7x) / 2 x = -8.5 + 3.5x

15. Nnesha

hmm you mean x = -8.5 +3.5 y right ?

16. calculusxy

yes sorry :)

17. Nnesha

its okay yep right

18. calculusxy

-5(-8.5 + 3.5y) - 8y = 17

19. calculusxy

42.5 - 17.5y - 8y = 17 42.5 - 25.5y = 17 -25.5 - 25.5y = 17 -25.5y = 42.5 y = 1.67 i am pretty sure i am wrong it's going on decimals.

20. Nnesha

well i don't understand the 3rd line

21. calculusxy

if i did 17 - 42.5 = -25.5

22. Nnesha

yep that's right you need to move 42.5 to the right side then you will get Perfect one

23. calculusxy

what do you mean by moving 42.5?

24. Nnesha

i meant you have to subtract 42.5 both sides :=)

25. Jacob902

correct

26. calculusxy

so what i did was correct right?

27. Nnesha

$$\color{blue}{\text{Originally Posted by}}$$ @calculusxy 42.5 - 17.5y - 8y = 17 42.5 - 25.5y = 17 -25.5 - 25.5y = 17 -25.5y = 42.5 y = 1.67 i am pretty sure i am wrong it's going on decimals. $$\color{blue}{\text{End of Quote}}$$ well here 3rd line you need to subtract 42.5 both sides i don't why there is -25.5 -25.5y

28. calculusxy

oh yeah

29. calculusxy

my mistake :\

30. Nnesha

:=) doing gREAT

31. calculusxy

y = 1 right?

32. Nnesha

yep right!

33. calculusxy

and then we would do: -5x - 8(1) = 17 -5x - 8 = 17 -5x = 25 x = -5

34. Nnesha

gO_OD to go!

35. calculusxy

thanks :) I have another question. it's small and related to basic physics. can u help?

36. Nnesha

PHYSICS hmmmm not sure

37. calculusxy

can u just see it? if u can't do it then u don't have to.

38. Nnesha

ye sure!

39. calculusxy

okay. here it is...

40. calculusxy

If i'm driving in a car at 30kph and a friend is driving in a car with the same mass at 60kph, my friend's car's kinetic energy is bigger than mine by a factor of what? (that is, divide my friend's over mine.)

41. Nnesha

i'm not sure havn't done physics n a while sorry

42. calculusxy

okay thank you though :)

43. Nnesha

np good job!