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Brooke_army

  • 3 years ago

If y=x3+5x and dx/dt=5, find dy/dt when x=2.

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  1. Brooke_army
    • 3 years ago
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    ok for this question i think im doing something wrong i got the answer of 17 but this is not right please help

  2. nubeer
    • 3 years ago
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    can you find dy/dx of the given equation?

  3. Brooke_army
    • 3 years ago
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    dy/dt=3x^2+5

  4. phi
    • 3 years ago
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    when you take the derivative wrt to t you should get a dx/dt term

  5. hartnn
    • 3 years ago
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    u need to use chain rule d/dt(5x) = 5 d/dx (dx/dt)

  6. phi
    • 3 years ago
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    instead of d/dx x^3 = 3 x^2 dx/dx you do d/dt x^3 = 3 x^2 dx/dt

  7. phi
    • 3 years ago
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    if you think \[ \frac{d}{dx} x= 1\] think this \[ \frac{ d}{dx} x= \frac{dx}{dx}= 1\]

  8. sunnymony
    • 3 years ago
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    |dw:1352559750685:dw|

  9. phi
    • 3 years ago
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    using the same logic \[ \frac{d }{dt} x= \frac{dx}{dt} \]

  10. sunnymony
    • 3 years ago
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    3x2+5 is ans

  11. Brooke_army
    • 3 years ago
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    thanks so much i got the wright answer!!

  12. sunnymony
    • 3 years ago
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    dy/dx= 3x2+5 dx/dt = 5 so both multiply we get =15x2+25

  13. phi
    • 3 years ago
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    then you got dy/dt=3x^2 dx/dt + 5 dx/dt replace x=2, dx/dt=5 to get dy/dt = 3*4*5+ 5*5= 85

  14. sunnymony
    • 3 years ago
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    so 15( 2x2)+25 =60+25 85

  15. sunnymony
    • 3 years ago
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    thats right @phi

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