Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

### Questions (36)

 31 What is the proof that covariance matrices are always semi-definite? 27 Affine transformation applied to a multivariate Gaussian random variable - what is the mean vector and covariance matrix of the new variable? 14 What is the general formula for calculating dot and cross products in spherical coordinates? 12 Could we show $1-(x-\frac{x^3}{3!}+\frac{x^5}{5!}-\dots)^2=(1-\frac{x^2}{2!}+\frac{x^4}{4!}- \dots)^2$ if we didn't know about Taylor Expansion? 11 Solving matrix equations of the form $X = AXA^T + C$

### Reputation (3,435)

 +10 How to check if a point is inside a rectangle? +10 Finding location of a point on 2D plane, given the distances to three other know points +10 What are the $\succ$ and $\prec$ operators for when used with matrices? +10 What is the proof that covariance matrices are always semi-definite?

 34 What is the proof that covariance matrices are always semi-definite? 29 Affine transformation applied to a multivariate Gaussian random variable - what is the mean vector and covariance matrix of the new variable? 27 Find five positive integers whose reciprocals sum to $1$ 17 Integration by substitution, why do we change the limits? 12 How to check if a point is inside a rectangle?

### Tags (82)

 35 matrices × 10 29 multivariable-calculus × 6 34 probability × 6 29 normal-distribution × 4 34 proof-writing × 5 29 random-variables × 4 34 vector-spaces × 2 29 linear-algebra × 4 34 positive-semidefinite × 2 27 diophantine-equations × 2