Multiplying Two Digits By Two Digits And Binomials Mentally

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Multiplying two digits by two digits and binomials by binomials mentally by Raiyan on December 25, 2008

Table of Contents intro: Multiplying two digits by two digits and binomials by binomials mentally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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step 1: 2 digit*2 digit mentally! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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step 2: Binomial*Binomial mentally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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intro: Multiplying two digits by two digits and binomials by binomials mentally How fast can you multiply 41*31 or (x+3) (x+7). Today you are going to learn to use the rainbow method.

step 1: 2 digit*2 digit mentally! How fast can you multiply 41*31 or (x+3) (x+7). Today you are going to learn to use the rainbow method. Now this can take less than ten second for multiplying two digits or even for binomial multiplication. 41*31 First multiply 4 and 3= 12 and 1 and 1=1. So we have the first digits and the last digit! 12_1. Now fill in the blank using rainbow multiplication. The innermost digits and the outer most digits. 4 and 1 is 4; 1 and 3 is 1! 4+3= 7. Answer is 1271. Now can you multiply 47*86 in just ten seconds? 4*8= 32 7*8= 56 4*6= 24 56 + 42 = 98 7*6= 42 84 3202 8+32 =40 4042= answer Practice More! Jumping ten Trick 43 + 56 = ?? Add the last digit of the smaller number. 43 + 6= 49 49+ 50= 99

step 2: Binomial*Binomial mentally Please review the last multiplication in the previous step. (x+4) (x+5) x*x= x squared Rainbow: 4x +5x= 9x 4*5= 20 Answer x squared +9x + 20 Another problem (x+7) (x+3) Answer= xsquared + 10x +21 To check: Coefficient plus seven (1 +7) = 8 coefficient (1) plus three (4) 8 times 4 is 32 Now 1 (coefficient) + 10 (coefficient) +21= 32 So now we are sure that I was correct. You see this is so fun!

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