**Example 1** If *a* = 2021, *b* = 2022 and *c* = 2023, find the value of the expression *a*^{2} + *b*^{2} + *c*^{2} – *ab* – *bc* – *ca*.

**Example 2** If the height of a triangle is decreased by 40% and its base is increased by 40%, what will be the percentage change in its area?

Of course, you should try/ solve these questions on your own and then check the solutions given.

**Solution 1**. If we put the data in a calculator, it will show as below:

Of course, the answer is 3. But how to do when a calculator is not available? To start with, look at the expression given in the question. Following probable questions may come to our mind:

(**i**) Is it possible to apply the formula of (*a *+ *b*)^{2} or (*a* − *b*)^{2} anyway?

(**ii**) Is it possible to rearrange the terms?

(**iii**) Can we do something, as there is a symmetry in the expression?

Yes, rearrangement is possible. Recall that, *first multiplying and then dividing by the same quantity* will result in no change. Applying these concepts, we have

**Solution 2**. Let the height and base of the triangle *ABC* be *h* and *b* respectively (see the figure below).

Now, the height of the triangle is decreased by 40% but its base is increased by 40%.