The most important result from last time was that if you took this r, and you took two derivatives of this to find the acceleration, d^2 r over dt^2, try to do this in your head.
上节课最重要的结论,就是如果你把 r 写成这样,对 r 求两次导就能得到加速度,d^2 r / dt^2,心算一下
This warning was transmitted in not one but two letters from Rep. Spencer Bachus (R-AL) and Rep. Dennis Kucinich (D-OH) on August 3, 1999 and November 8, 1999.