this is fucked up. this fucked me up. the teachers fucked up by not showing us this fuck up. fuck.
i’m 28 and never knew this
This is… just simple decomposition and binomial multiplication (see FOIL method), represented by lines. The teachers did not fuck up if you learned how to do long multiplication.
21*13 = (20+1)*(10+3) = (20*10)+(20*3)+(1*10)+(1*3)
It’s nice seeing a graphical representation, but once you get to larger digits it’s going to take much less time to just decompose and multiply than draw lines. Who wants to draw out and count 95*56? It’s 4500+250+540+30 = 5320. That took no time.
Understanding what you are doing is far better than graphical tricks that look like magic.