Question 1186790
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All edges of a cube are expanding at a rate of 5 centimeters per second.

(a) How fast is the surface area changing when each edge is 3 centimeters?

(b) How fast is the surface area changing when each edge is 10 centimeters?
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<pre>
The surface area  of a cube is  A = {{{6a^2}}}, where "a" is the edge measure.


  (a)  the rate of change the surface area of the cube is


           {{{(dA)/(dt)}}} = {{{6*2a*((da)/(dt))}}}  cm^2 per second.


       Now substitute given values  a = 3 cm,  {{{(da)/(dt)}}} = 5 cm per second into the formula and get

           {{{(dA)/(dt)}}} = {{{6*2a*((da)/(dt))}}} = {{{12*3*5}}} = 180  cm^2 per second.    <U>ANSWER</U>




  (b)  Solve  it by the same way as (a)
</pre>

Solved.