Quote:
Originally Posted by seiki
I just learned this today in math class and I am finding it fascinating. We talked about how .999999 with a repeating decimal equals 1. And did a proof for it. It was awesome.
It was crazy are there any other things like that in math?
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The current US federal budget or lack of ^^/
No but really:
Squaring a 2 digit number ending in the number 5.
65*65
1. Multiply the first digit one more than itself. (in this example one more than 6 is 7)
6*7 = 42
2. Put 25 after the answer. The answer will always end in 25.
65*65 = 4225
How is this done?
Squaring a binomial. It only works however when the number you are squaring ends in 5.
1 = ............................................1= 1*1
1+
2+1 =.....................................4 =2*2
1+2+
3+2+1=..............................9 =3*3
1+2+3+
4+3+2+1=..................... 16=4*4
1+2+3+4+
5+4+3+2+1=..............25=5*5
and so on
I like math parlor tricks.