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 Oct 15 awarded Popular Question Jun 7 awarded Nice Answer Dec 8 awarded Caucus Sep 15 comment Binomial Theorem Application Exercise Hint: $\binom{n}{k}2^{n-k}=\binom{n}{k}\left(1+1\right)^{n-k}=\sum_{j=0}^{n-k}\binom{n‌​}{k}\binom{n-k}{j}$. May 28 answered If $P(x) = ax^2 + bx + c$ and $Q(x) = -ax^2 + dx + c$, then prove that $P(x) \cdot Q(x) = 0$ has at least two real roots? Mar 25 awarded Critic Nov 16 comment Lottery probability question… Second place needs to capture exactly five of the six numbers. How many ways can this be done? The denominator remains the same: there are still $\binom{59}{6}$ ways to draw six numbers from 59. However, the numerator should count the number of ways you may draw five numbers from the winning six and one number from the remaining 53 numbers. May 15 awarded Caucus Feb 24 comment Given $x(t) = u(t)$ and $h(t) = \cos(\pi t)u(t)$, how do we find the response $y(t)$? I don't see why the integral isn't $\int_{0}^{\infty}cos(\pi\tau)u(\tau)u(t-\tau)d\tau$. Nov 7 answered Poisson Distribution for Consecutive Figures Nov 2 comment Solve $Ax = b$ where $b$ are labels instead of values @locke14 I misunderstood the question. My response was for $A$ having these entries, not $b$. Nov 2 comment Solve $Ax = b$ where $b$ are labels instead of values Usually with categorical variables, one category is chosen as a baseline and all others are assigned their own indicator variable in the regression. For example, if the original variable represents weight and the categories are "low", "medium" and "high", we may choose "medium" as the baseline and create two other variables named "isLow" and "isHigh". If a person has "medium" weight, isLow and isHigh will both be zero. If a person has "low" weight, isLow will be one and isHigh will be zero. If a person has "high" weight, isLow will be zero and isHigh will be one. Oct 30 comment Process for $(k+1)^3$? @wj32 Ah. That makes sense. Oct 30 comment Process for $(k+1)^3$? You don't mention the binomial theorem anywhere in your question. Oct 30 comment Process for $(k+1)^3$? Look into the binomial theorem. Oct 28 comment Puzzle on Ranks The computation is correct. This is a good way of thinking about the problem though. Oct 26 accepted Help Needed: Partial Derivative Identity/Chain Rule Oct 26 comment Formulas for the multivariate Gaussian function? If you convert the density function to use the actual elements of $x$ and $\Sigma$ rather than the matrix equivalents, taking derivatives will become more clear. Oct 17 comment Calculating Variance of a binomial distribution using the standard formula $E(X^2) - \mu^2$ Yes, that is correct. Oct 17 revised Calculating Variance of a binomial distribution using the standard formula $E(X^2) - \mu^2$ added 186 characters in body