Find the approximate change in the surface area of a cube of side x metres caused by decreasing the side by 2%

  1.  0.23x2 m2
  2.  0.21x2 m2
  3.  0.22x2 m2
  4.  0.24x2 m2

Answer (Detailed Solution Below)

Option 4 :  0.24x2 m2
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General Knowledge for All Defence Exams (शूरवीर): Special Live Test
20 Qs. 20 Marks 16 Mins

Detailed Solution

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Concept:

Let the side of the cube is x meters,

Surface area of cube = S = 6 × (side)2

Approximate change in the surface area of the cube is given by: 

Calculation:

Given: Side of the cube = x metres

Decrease in the side of cube = Δx = -2% of x            (Negative sign indicate decreasing the quantity)

⇒ Δx = -0.02x

Now, Surface area of a cube is given by,

 S = 6 × (side)2 = 6x2

Differentiating with respect to x, we get

⇒ 

Now,

The approximate change in the surface area of a cube = 

Hence, the approximate change in the surface area of a cube is 0.24x2 metres2

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