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Definite integrals
Krystian Karczyński

The Volume of an Ellipsoid (But Not a Rotational One, Just a Wild Type) Calculated by a Definite Integral

Let’s say we need to calculate the volume of an ellipsoid: {x^2}/4+{y^2}/5+{z^2}/9=1. This is an ellipsoid that intersects the x, y, z axes at coordinates 2, \sqrt{5}, and 3, respectively.

This is not a rotational ellipsoid, it is not formed by rotating any curve around any axis, so we can’t use the standard formula for the volume of a rotational solid. We need to figure out another way.

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Complex numbers
Krystian Karczyński

What to Do When Exponentiation Just Doesn’t Work (Complex Numbers)

There are days when nothing seems to work. And there are examples with complex numbers where nothing goes right. The known and memorized methods don’t help.

Take, for instance, this innocent-looking exponentiation: (1+2i)^8. Following the well-trodden path you’ve used in many examples, you want to write the number 1+2i in trigonometric form and then raise it to the eighth power using the appropriate formula. But you encounter complications along the way… See the trick I use.

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Limit of a sequence
Krystian Karczyński

Limits with Cube Roots (Is it Multiplication by Conjugate?)

When given a limit to calculate that involves some subtraction with a root (and which obviously couldn’t be calculated more simply), such as: “Something – square root of something”, “square root of something – Something”, or “square root of something – square root of something”, we used a trick I call – “multiplication by the conjugate.”

We simply multiplied this expression by its counterpart with a plus sign, or rather by a fraction where this counterpart was in the numerator and the denominator.

What to do when the roots are cube roots?

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