Comments on Homeschool Math Blog: Math trick and its proof: square a number ending i...

Glad you liked the post. That's the best thing ab...

2009-09-04T10:33:50.424-04:00

Glad you liked the post. That's the best thing about math tricks, is they're all provable, or they wouldn't work!

I learned this trick in High School. Thanks for th...

2009-09-02T14:41:33.480-04:00

I learned this trick in High School. Thanks for the formal proof.

the explanation of the 'trick' itself could use a ...

2009-09-01T20:05:42.540-04:00

the explanation of the 'trick' itself could use a little work - use a graphic program to step it out more clearly by circling the bits you are referring to at each step of the algorithm.

the proof is clear.

Marla, This can be generalized to any numbers as ...

2009-08-29T19:44:05.603-04:00

Marla,
This can be generalized to any numbers as long as the tens digits are the same and the last two are tens compliments... ie 75x75=5635 74x76 =564 and 73x77=5621...

and if you learn a simple rule for multiplying any two numbers in the teens, you can extend it up to 195x195
for example, to multiply 14x15 you add 14+5 (or 15+4) for the number of tens (ie 190) then and the product of hte last two digits (5x4=20) to get 210
s0 145x145=210___25

a second example, to do 175^3 we do 17x18 = 17+8 = 25 tens or 250 and then add 7x8=56 to get 306, now tack on the 25 to get 175^2=30625...
there is also an easy way to multiply numbers in the twentys..etc...