Question

when should we add or subtract base area (surface area and volume class 10th) ​

Answer 1

Answer:

It is a little tricky to find out in the beginning when and how to subtract the base areas in the TSA - CSA ( Lateral Surface Area in case of cubes, cuboids) related questions (Concerning cubes, cuboids, cones and cylinders).

Here is the key to the confusion.

a. In a question, when you are asked to find out the CSA or lateral surface area, then you are asked to exclude the area of base and top.

b. In a question, when you are asked to find out the TSA, then you are asked to add the areas of base and the top of a three-dimensional figure.

c. In questions when there is a TSA given and you are asked to calculate CSA or lateral surface area, then, simply remove the areas of the base and top.

I hope, this helps you.

Answer 2

Answer

While calculating TSA we should add base area and while calculating CSA then we need to exclude base area.

Explanation

1) If in any question we are asked to find out CSA or lateral surface area then we are supposed to exclude the area of top and bottom.

For example

CSA of cone = πrl

CSA of cylinde = 2πrh

2) If in any question we are asked to find the total surface area TSA when we are supposed to include the area of top and bottom.

For example
TSA of cone = πrl + πr² = πr(l+r)

TSA of cylinde = 2πrh + πr² + πr² = 2πr(h+r)

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