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A radioactive substance is subject to th...

A radioactive substance is subject to the law of natural decay `(dv)/(dt)=-kv`, where v is the volume of the substance at time t and k is a positive constant. The half-life of the substance is the time it takes for half the substance to disappear. Calcualte the half-life if 20 % of the substance disappeared in 15 years.

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A DAS GUPTA-Differential Equation of the First Order-Exercise
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  3. A radioactive substance is subject to the law of natural decay (dv)/(d...

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  7. Find the equation of the curve such that the square of the intercept c...

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  8. Find the curves for which the length of normal is equal to the radius ...

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  9. Find the cartesian equation of the curves for which the length of the ...

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  10. Find the equation of the curve for which the length of the normal is c...

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  11. Find the equation of the curve which is such that the area of the rect...

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  14. The normal PG to a curve meets the x-axis in G. If the distance of G f...

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  15. Find the equation of curves for which the cartesian subtangent varies ...

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  16. Find the equation of the curve in which the subnormal varies as the ...

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  17. Find the orthogonal trajectory of y^2=4a x (a being the parameter).

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  18. Prove that the family of curves x^2/(a^2+lambda)+y^2/(b^2+lambda)=1, w...

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  19. For the differential equation sqrt(1+(d^2y)/(dx^2))=x, the degree=and ...

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  20. If the general solution of a differential equation is (y+c)^2=cx, wher...

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