Homework Help: calculus

Posted by Pam on Friday, April 25, 2008 at 7:59am.

Please help, my live tutor and I could spent 2 hours trying to solve these two:
find an equation for tangent line y=-1-8^2@ (-4,-129)

find the derivative of the function:----we both kept getting the same answer, but Mathlab kept saying that it was wrong: -4lnl3xl/2+3x
we did the quotient rule, and the chain rule...the derivative and our sign would be wrong...

calculus - Reiny, Friday, April 25, 2008 at 8:21am
I cannot make sense out of your equation, check your typing.
- calculus - Pam, Friday, April 25, 2008 at 11:39am
  -4 ln l3xl
  2+3x
  -4ln absolute value of 3x over 2+3x
  
  y= -1-8x^2
  (-4,-129)
  the first set is in fraction form.
  the 3x is absolute.
  the 8x^2 is 8x squared.
calculus - Reiny, Friday, April 25, 2008 at 12:33pm
for the derivative using the quotient rule I got (-8 - 12x + 12x(ln(3x))) / (x(2+3x)^2)

for the tangent question
dy/dx = -16x

at the point the slope is -16(-4) = 64

so using y = mx + b for the tangent equation
-129 = 64(-4) + b
b = 127

so the tangent equation is y = 64x + 127
- calculus - Pam, Friday, April 25, 2008 at 12:45pm
  Thanks. One small error? I can see what we did wrong..we did not do the
  -129= part.....guess we were tired, or tried to do it in our heads.

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