Besides Riemman sums and the substitution method, how can i estimate the area under the curve for these problems? I was able to find the area using the substitution method, but my TA mentioned how there is a quicker way to estimate the area . He said something about drawing a box, and he used inequalities to represent the area?

Also, i heard that all the areas are equal and that they are equal to 2.

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https://imgur.com/a/9K1rw