I encountered an question of calculation of volume. The following is a part of the solution. I don't know why the highlighted sinθ has an absolute value sign. Can anyone explain to me? Thank you.

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Because $\displaystyle \sqrt{a^2}= |a|$, not a. For example, $\displaystyle \sqrt{(-2)^2}= \sqrt{4}= 2$, not $\displaystyle -2$.

Thank you, HallsofIvy.

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