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Rates of change: The rate of change of the area of a triangle. Is my answer right?

  1. Jun 10, 2012 #1
    my question is... is this answer correct? for the last step. WOULDNT you multiply 10x by .5 and 12 by .2? the opposite of what this answer is? Itsays BASE is 10 in and BASE chagnges at .5 in per second
    problem:
    i45.tinypic.com/xknbci.png
    answer:
    i50.tinypic.com/2qcnsyv.jpg

    this is what i get...

    i50.tinypic.com/124cxgy.jpg
     
  2. jcsd
  3. Jun 10, 2012 #2

    SammyS

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    Staff Emeritus
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    Re: Rates of change: The rate of change of the area of a triangle. Is my answer rig

    Hello indigo1. Welcome to PF !

    Why would you want to multiply the base by the rate of change of the base? Even your working has [itex]\displaystyle b\frac{dh}{dt}[/itex] and [itex]\displaystyle h\frac{db}{dt}\ .[/itex]

    dh/dt is -0.2 in/sec and db/dt is 0.5 in/sec !

    BTW: Below are your images, displayed so others can see them.

    attachment.php?attachmentid=48210&stc=1&d=1339361547.png

    attachment.php?attachmentid=48211&stc=1&d=1339361619.jpg

    attachment.php?attachmentid=48212&stc=1&d=1339361660.jpg
     

    Attached Files:

  4. Feb 23, 2014 #3
    This was really helpful
    But i was wondering if this is the same for my HW problem i applied the same A' equation but instead looked for the db/dt and i got -3/2 idk if this is right.
    "The base of an isosceles triangle is 6 feet. If the altitude is 4 feet and increasing at the rate of 2 inches per minute, at what rate is the vertex angle changing?"
    I will really appreciate for your help.
     
  5. Feb 23, 2014 #4

    Mark44

    Staff: Mentor

    seawolf23, instead of tacking your question onto the end of a question from almost two years ago, please start a new thread. Be sure to use the homework template, and include the problem statement and the work you have done.
     
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