** A sporting goods store sells 90 ski jackets in a season for $275 each. Each $15 decrease in the price results in five more jackets being sold. What is ...

I don't understand where that formula came from. Could someone explain? For example any point $(x,y)$ on the ellipse from the two foci $(-c,0)$ and $...

The order of the groups does not matter The size of group must be at least 1 For example, in a more specific question How many ways to split 5 number in 2...

I would like an efficient algorithm for square root of a positive integer. Is there a reference that compares various square root algorithms? Thanks.

Using the fact that $x^2 + 2xy + y^2 = (x + y)^2 \ge 0$, show that the assumption $x^2 + xy + y^2 < 0$ leads to a contradiction... So do I start off wi...

How do you take the derivative of the following function: $$y=\ln(|\sec(5x) + \tan(5x)|)$$ So $dy/dx$ of the following function. Thanks in advance! The st...

I see two different formulae. https://www.comp.nus.edu.sg/~cs5240/lecture/matrix-differentiation-c.pdf In this slides page 9, the derivative of $Ax$ is $A...

Find the number of subsets of the set $\{1,2,3,\ldots,10\}$ that contain $4$ elements and do not include any pair of consecutive numbers. For example $\{1...

i am faced with the following problem which i can't seem to solve... Let $X_1$ and $X_2$ two independent normal distributions of parameters $\mu$ and...

Apologies if there is a duplicate somewhere; I couldn't find one. The use of the root "deriv" in the context of differentiation seems odd: we have di...