• ## [Crimson Boy Can You Solve This?] [0] easy algebra

This is an easy algebra problem. I believe clever jgh must can solve it in 1min! We know that x-\frac{y}{z}-\frac{z}{y}=y-\frac{x}{z}-\frac{z}{x}=z-\frac{x}{y}-\frac{y}{x}=a and x {\neq}y{\neq}z (1) What is the value of x+y+z ? (2) What is the valu……
HDD 2020-01-05
• ## INM season 2 ended!!!

INM has ended!!!!! Oh, what a season! Although this season's very short, we did pretty many things and seems it's better than INM season 1. Thanks to all member's efforts! What we did: super slow exp machine super slow slime farm not so slow iron ……
HDD 2019-08-31

$1.\int{\frac{1}{\sqrt{x^2±a^2}}}dx=ln|x+\sqrt{x^2+a^2}|+C(a>0)$ $1.5.特别地, \int{\frac{1}{\sqrt{x(x+a)}}}dx=ln(\sqrt{x}+\sqrt{x+a})+C(a>0)$ $2.\int{tan^2(x)}dx=tanx-x+C$ $3.\int{\frac{1}{x^2+a^2}}dx=\frac{arctan{(\frac{x}{a})}}{a}+C$ $4.\int{\fra…… HDD 2019-08-31 • ## [小题狂做]欧拉公式与暴力展开（1） 由于这篇blog语言儒雅随和通俗易懂，所以一般通过观众也可以放心观看 例题（著名题）：$\int^{\infty}{0}{\frac{{e^{cosx}}{sin(sinx)}}{x}}dx这道题乍一看很复杂，当时我也想了十万甚至九万分钟，但其实在回顾过3B1B的傅里叶变换后，才发现这是一道可以用傅里叶级……
HDD 2019-04-21
• ## 公式测试

$$e^{ix}=cosx+isinx$$ $$\int_0^{\infty} {\frac{sinx}{x}} {\rm d}x=\frac {\pi}{2}$$ $$\iint {f(x,y)d\sigma}=\int{d\theta}\int{f(r,\theta)dr}$$ $$wordpress nmsl$$
HDD 2019-04-07
• ## 回应赵宇“气”的问题

我佛了，空气阻力太难力 111 空气阻力F=kv^2 所以1° 上升时 F=-kv^2-mg dv/dt=-kv^2/m-g ∫(-1/kv^2/m+g)dv=t+v0 左边应该事arctan,所以v=-tanCt+v0，，， 2° 下降时 F=mg-kv^2 ∫(1/mg-kv^2)dv=t+C 有理分式，平方差暴力拆拆↑ 答案应该与e……
HDD 2019-04-07
• ## 高斯(dick)积分

是我，高斯男孩 e**** d*** integral ∫(-inf,inf)e^(-x^2)dx ← 这事高斯积分 原式^2 =∫(-inf,inf)e^(-x^2)dx*∫(-inf,inf)e^(-y^2)dy =∬e^(-x^2-y^2)dσ D={(x,y)|x∈R,y∈R} = ∫dθ∫re^(-r^2*sin^2θ-r^2*cos^2)dr D={(r,θ)|r∈[0,inf),θ∈[0,2π]} =∫dθ∫re^(-r^……
HDD 2019-04-05