Question

A box has the shape of a rectangular prism with height 30 cm. If the height is increased by 0.9 ​cm, by how much does the surface area of the box​ increase?
Use pencil and paper. Show your work. Then show a second way to solve the problem. Explain which way you like better and why.

Answer 1

Answer:

The corresponding increase in surface area of the rectangular prism for an increase of 0.9 cm in height is given by

ΔS = [1.8 (L + B)] cm

where L = length of the rectangular prism

B = Breadth of the rectangular prism

Step-by-step explanation:

A rectangular prism is essentially a cuboid.

The surface area of the cuboid is given as

S = 2[LB + LH + BH]

where

L = length of the rectangular prism

B = Breadth of the rectangular prism

H = Height of the rectangular prism

S = 2LB + 2LH + 2BH

Derivative explains that, for small changes in the two quantities,

(∂S/∂H) = (ΔS/ΔH)

ΔS = ΔH × (∂S/∂H)

S = 2LB + 2LH + 2BH

(∂S/∂H) = 2L + 2B = 2(L + B)

ΔH = 0.9 cm

ΔS = ΔH × (∂S/∂H)

ΔS = 0.9 × 2(L + B) = 1.8 (L + B)

A rectangular prism is essentially a cuboid.

The surface area of the cuboid is given as

S = 2[LB + LH + BH]

where

L = length of the rectangular prism

B = Breadth of the rectangular prism

H = Height of the rectangular prism

S = 2LB + 2LH + 2BH

If the height of the rectangular prism increases by 0.9 cm

S(new) = (2×L×B) + 2L(H + 0.9) + 2B(H + 0.9)

S(new) = 2LB + 2LH + 1.8L + 2BH + 1.8B

S(new) = 2LB + 2LH + 2BH + 1.8L + 1.8B

The old surface area, S = 2LB + 2LH + 2BH

Hence, the change or increase in surface area is S(new) - S

[2LB + 2LH + 2BH + 1.8L + 1.8B] - [2LB + 2LH + 2BH] = 1.8L + 1.8B = 1.8 (L + B)

Still the same increase in surface area as obtained by the first method.

Hope this Helps!!!