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anonymous

  • one year ago

Algebraic expressions.. Evaluate 3x-y2 for x = -3/4 and y = -2/5

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  1. welshfella
    • one year ago
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    you replace x by -3/4 and y by -2/5 in the expression and work it out. = 3*(-3/4) - (-2/5)^2

  2. anonymous
    • one year ago
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    I know i plug it it in so it would be 3(-3/4) - (-2/5)^2 right?

  3. welshfella
    • one year ago
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    yes

  4. anonymous
    • one year ago
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    i dont like working with fractions i always get confused

  5. welshfella
    • one year ago
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    multiplying fractions is not too difficult just multiply top and bottom:- |dw:1440933535144:dw|

  6. welshfella
    • one year ago
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    * thats 15 not 35!!

  7. anonymous
    • one year ago
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    is there more steps?

  8. welshfella
    • one year ago
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    yes do the multiplication and squaring first finally subtract

  9. anonymous
    • one year ago
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    hmm

  10. welshfella
    • one year ago
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    |dw:1440933718810:dw|

  11. anonymous
    • one year ago
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    the first one was just an example right?

  12. welshfella
    • one year ago
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    yes

  13. anonymous
    • one year ago
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    ok :)

  14. anonymous
    • one year ago
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    do i multiply the 4 and -3

  15. anonymous
    • one year ago
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    and then add the 3

  16. welshfella
    • one year ago
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    no - multiply the top numbers that is -3 and 3

  17. anonymous
    • one year ago
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    oh okay!

  18. anonymous
    • one year ago
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    okay i got 9/4 - 4/25 is it wrong?

  19. welshfella
    • one year ago
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    no that is correct

  20. anonymous
    • one year ago
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    and then i subtract?

  21. anonymous
    • one year ago
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    or multiply

  22. anonymous
    • one year ago
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    the answer on the worksheet says its -2 41/100|dw:1440934161182:dw|

  23. welshfella
    • one year ago
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    notice that 9/4 is an improper fraction I ts easier at this stage to convert iutto a mixed number 9 divide by 4 is 2 and there is a remainder 1 so 9/4 = 2 1/4

  24. anonymous
    • one year ago
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    oh!

  25. welshfella
    • one year ago
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    so we have |dw:1440934184640:dw|

  26. anonymous
    • one year ago
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    got it

  27. welshfella
    • one year ago
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    sorry it was negative -9/4 - 4/25 not 9/4 - 4/25

  28. anonymous
    • one year ago
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    its okay

  29. welshfella
    • one year ago
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    now you can only subtract and add fractions withe the same denomiantor so you need to find the LCD (Lowest Common Denominator) of 4 and 25

  30. welshfella
    • one year ago
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    LCD of 4 and 25 is 100

  31. anonymous
    • one year ago
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    yes it is

  32. welshfella
    • one year ago
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    so converting 1/4 to hundredths we multiply the top ond bottom of the fraction by 15 |dw:1440934433350:dw|

  33. anonymous
    • one year ago
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    does the 2 dissapear?

  34. welshfella
    • one year ago
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    and |dw:1440934510629:dw|

  35. welshfella
    • one year ago
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    No we'll bring that in at the end

  36. welshfella
    • one year ago
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    so we have now got |dw:1440934591025:dw|

  37. anonymous
    • one year ago
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    OH!! I understand now :) thanks so much!

  38. welshfella
    • one year ago
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    good Try and practice some more problems of same type and you'll gain confidence

  39. welshfella
    • one year ago
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    fractions are a bit tricky

  40. anonymous
    • one year ago
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    yes i will thank you!

  41. welshfella
    • one year ago
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    yw

  42. anonymous
    • one year ago
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    okay i just tried figuring out how to get 41 do you subtract the 25 and 10?

  43. welshfella
    • one year ago
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    - and watch the negatives - i forgot them a few times myself!

  44. welshfella
    • one year ago
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    no -16 - 25 = -41

  45. anonymous
    • one year ago
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    you add 2 to 25 and add 2 to 10? and that gives you 39? and -2 + 41 = 39

  46. anonymous
    • one year ago
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    oh

  47. anonymous
    • one year ago
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    i thought that was a 10 sorry

  48. welshfella
    • one year ago
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    you are really adding negative numbers -16 + (-25) = -41 Tha'ts what makes this one extra tricky - you have negatives and fractions..

  49. welshfella
    • one year ago
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    - thats my bad drawing

  50. anonymous
    • one year ago
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    Okay i just checked my work :)

  51. welshfella
    • one year ago
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    lets try -3/16 - 7 / 16 what does that equal?

  52. welshfella
    • one year ago
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    -3 - 7 = ?

  53. anonymous
    • one year ago
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    -10?

  54. welshfella
    • one year ago
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    yea so its -10/16 when add/subtract the denominator stays the same

  55. anonymous
    • one year ago
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    yeah i always get confused by negatives

  56. welshfella
    • one year ago
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    Practice

  57. anonymous
    • one year ago
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    Thanks again :)

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