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Math Help - Slope

  1. #1
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    Slope

    y= 2x^2 + 3x

    a) i need to find the slope at x= -2
    b) then i need to find the equation of the tangent line at x= -2
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  2. #2
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    Differentiate the equation and get the value of y' in terms of "x"

    1)Find value of y'(-2) by putting x = -2

    2)
    at x = -2 , y=?

    the equation of tangent can be given by

    y= mx+c

    this euation should satisfy the for the point (-2,?)

    , you know the value of m [it is, y'(-2) ]

    use this two facts to find "c"

    Hence equation is with you
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  3. #3
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    4x+3 = m = -5

    y= mx + c = c = -12

    y= -5x-12

    can somebody confirm if this is correct?
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  4. #4
    Like a stone-audioslave ADARSH's Avatar
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    Quote Originally Posted by makaveli89 View Post
    4x+3 = m = -5

    y= mx + c = c = -12

    y= -5x-12

    can somebody confirm if this is correct?
    No its Not correct

    y = -5x +c

    At x =-2

    y = 2(-2)^2 + 3(-2)

    =8-6 = 2
    this gives a point (-2,2) on the curve
    So the tangent will pass through this point and hence this point satisfies its equation

    y = -5x+c will pass through (-2,2)

    2=10+c

    c=-8

    Hence thew complete equation is
    y=-5x-8
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