Don't Substitute!

Algebra Level 2

Find the value of

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c , 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc,

when a = 888 a = 888 , b = 666 b = 666 , and c = 444 c = 444

Hint: Try to simplify


The answer is 1579654321.

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2 solutions

Syed Hamza Khalid
Jul 27, 2017

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc

Well lets make a new letter named d d which is equal to 222 222 , So it means that:

a = 4 d a = 4d

b = 3 d b = 3d

c = 2 d c = 2d

Now simplifying the above expression using these codes will make it:

1 + 4 d + 2 ( 3 d ) + 3 ( 2 d ) + 2 ( 4 d ) ( 3 d ) + 3 ( 4 d ) ( 2 d ) + 6 ( 4 d ) ( 3 d ) ( 2 d ) 1 + 4d + 2(3d) + 3(2d) + 2(4d)(3d) + 3(4d)(2d) + 6(4d)(3d)(2d)

1 + 4 d + 6 d + 6 d + 24 d 2 + 24 d 2 + 36 d 2 + 144 d 3 1 + 4d + 6d + 6d + 24d^2 + 24d^2 + 36d^2 + 144d^3

1 + 16 d + 84 d 2 + 144 d 3 1 + 16d + 84d^2 + 144d^3

Now we can simply substitute the value of d into this equation:

1 + 16 d + 84 d 2 + 144 d 3 1 + 16d + 84d^2 + 144d^3

which can be factorized into:

( 4 d + 1 ) ( 6 d + 1 ) 2 (4d +1)(6d +1)^2

Now we can substitute 222 222 into the expression:

( 4 ( 222 ) + 1 ) ( 6 ( 222 ) + 1 ) 2 (4(222) +1)(6(222) +1)^2

Which is equal to

= 1579654321 =1579654321

Notice that 144 d 3 + 84 d 2 + 16 d + 1 = ( 4 d + 1 ) ( 6 d + 1 ) 2 144d^3+84d^2+16d+1 = (4d+1)(6d+1)^2 . This extra factorisation reduces the problem to multiplying 1 1 3 3 -digit number, 1 1 4 4 -digit number, and another 4 4 digit number.

Toby M - 3 years, 10 months ago

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Yeah ! Thanks. Good idea. I will have it changed soon.

Syed Hamza Khalid - 3 years, 9 months ago

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1+a+2b+3c+2ab+3ac+6bc+6abc

= ( a + 1 ) ( 2 b + 1 ) ( 3 c + 1 ) = ( 888 + 1 ) ( 2 666 + 1 ) ( 3 444 + 1 ) =(a+1)(2b+1)(3c+1)=(888+1)(2*666+1)(3*444+1)

= 889 1333 1333 = 1579654321 =889*1333*1333=\boxed{1579654321}

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