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anonymous

  • one year ago

Find the slope intercept form of the line whose slope is 4 and that passes through the point (-7,8) the equation of the line is?

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  1. MrNood
    • one year ago
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    you know that the slope - intercept equation looks like this: y=mx+b OK?

  2. anonymous
    • one year ago
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    Yes...

  3. anonymous
    • one year ago
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    That's as far as I understand... I don't know how to get the answer.

  4. MrNood
    • one year ago
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    ok well the 'm' in that equation is the slope the question tells oyu the slope so can you start to write the equation - putting th ecorrect value for m (but leave 'b' for now...)

  5. anonymous
    • one year ago
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    Y=4x

  6. MrNood
    • one year ago
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    y = mx +b m = 4 so write the equation with the value for m in it

  7. MrNood
    • one year ago
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    (you need the "+b" on the end )

  8. anonymous
    • one year ago
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    Ok. How do you get b?

  9. anonymous
    • one year ago
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    Oh, y=4x+b

  10. MrNood
    • one year ago
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    at the moment I just wanted you to write the equation like this y = 4x+b we still need to find b OK? - we are doing this in 2 steps - you have done one of them so far Do oyu understand why the equation starts to be y=4x+b ?

  11. anonymous
    • one year ago
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    Yes..

  12. MrNood
    • one year ago
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    OK good So now the second step is to use the second bit of information from the question that is the point (-7,8) lise on the line this means that the equation is true when x=-7, and y = 8 so write the equation y = 4x+b with the values x= -7 and y = 8 in it (leave b as it is for now)

  13. anonymous
    • one year ago
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    Okay..

  14. MrNood
    • one year ago
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    so write the equation y = 4x+b x= -7 y = 8 in it (leave b as it is for now)

  15. anonymous
    • one year ago
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    Y=4x+b y =8x=-7 this doesn't make sense to me..

  16. MrNood
    • one year ago
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    wherever there is y in the equation write 8 wherever there is x write -7 (BUT remember that 4x means 4 times x)

  17. anonymous
    • one year ago
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    8=4-7+b yes?

  18. anonymous
    • one year ago
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    B=5

  19. MrNood
    • one year ago
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    yes - but to be clear about 4 times x it is clearer if oyu write 8 = 4(-7) +b

  20. anonymous
    • one year ago
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    Y=4(-7)+5. Yes?

  21. MrNood
    • one year ago
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    yes so that can be rewritten as 8= -28 +b so what is b?

  22. anonymous
    • one year ago
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    Okay.. So I don't need it to equal 5?

  23. anonymous
    • one year ago
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    B is 5 no??

  24. MrNood
    • one year ago
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    no it's not , please don't rush - I am trying to guide you to work out the answer

  25. anonymous
    • one year ago
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    Okay I see..

  26. anonymous
    • one year ago
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    Sorry..

  27. MrNood
    • one year ago
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    To review what we did.. we KNOW the equation will be in th eform y = mx + b and we know that m is th eslope and we know the slope is 4 so we know th eequaiton is y= 4x+b BUT we also know that the point (-7,8) is on the line (which means the equationis true when it passes through that point) SO we know that when x = -7 then y = 8 so back to the equation we put y - 8 and x = -7 so 8=4×(−7)+b this is the same as 8 = -28 + b so you can work out b

  28. anonymous
    • one year ago
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    Yes... B =36

  29. MrNood
    • one year ago
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    well done so now write the whole equation y=mx+b with the values for m and b that you calculated

  30. anonymous
    • one year ago
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    Y=4x+36

  31. anonymous
    • one year ago
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    Correct ?

  32. MrNood
    • one year ago
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    correct well done this is the principle of all these questions - once you know the slope, you can use 1 point on the line to find b

  33. anonymous
    • one year ago
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    Thank you sir

  34. anonymous
    • one year ago
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    So, I attempted my next one and the slope is 7 the point is (-4,11). I came up with y=7x+35 but I was wrong it is 39 and I don't know where I went wrong??

  35. MrNood
    • one year ago
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    ok you made a good attempt starting with y = 7x + b then we put in the point values 11= 7 (-4) +b 11 = -28 +b you can see that 39 is the correct value

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