Sum of Coefifcients in Binomial? (1 Viewer)

[Watsername]

How would you do this question:

Find the sum of the cooeficients in (8a - 5b)^17

The answer is huge

 

[haboozin]

How would you do this question:

Find the sum of the cooeficients in (8a - 5b)^17

The answer is huge

8^17 - 17c1x8^16x5 + 17c2x8^15x5^2 - ... .... - 5^17

i dont really see any easier way of doing this? :s
what a silly question.

 

[KFunk]

One thing you could do to make life easier is to take a factor of 8¹⁷ out:

8¹⁷[1 - ¹⁷C₁(5/8) + ¹⁷C₂(5/8)² - ¹⁷C₃(5/8)³ + ... - (5/8)¹⁷]

If you kept (5/8) on the [ANS] - previous answer button then you could save your self a lot of button bashing. What a smelly question.

 

[Dreamerish*~]

One thing you could do to make life easier is to take a factor of 8¹⁷ out:

8¹⁷[1 - ¹⁷C₁(5/8) + ¹⁷C₂(5/8)² - ¹⁷C₃(5/8)³ + ... - (5/8)¹⁷]

If you kept (5/8) on the [ANS] - previous answer button then you could save your self a lot of button bashing. What a smelly question.

That's really smart. Why am I not surprised it came from you?

 

[Watsername]

yeh, thats exactly what i started writing out, and then I thought I must be missing something you surely going to make a mistake on your calculator during that

 

[haboozin]

yeh, thats exactly what i started writing out, and then I thought I must be missing something you surely going to make a mistake on your calculator during that

thats why you would never be asked this question...

you might be asked one that the sum of coefficients are zero

 

[currysauce]

How would you do this question:

Find the sum of the cooeficients in (8a - 5b)^17

The answer is huge

Isn't there a rule for sum of the coefficients

(a+x) ^ n is 2^n

 

[Templar]

Let a, b be equal to one maybe?

 

[KFunk]

Let a, b be equal to one maybe?

Ahh, there's the trick.

 

[zozo]

i wouldnt worry about it too much, its a beast of a questoin, the HSC just wouldnt ask it... at least not to the power of 17... maybe 4.

if you did ever get presented with a question like that in HSC, you'd be better to throw down some working out and move on, cause its only gonna be worth 1 or 2 marks tops... why waste 5 min when you milk 5 more marks in that time.

 

[acmilan]

Its really quite simple, and Templar explained it. Just make a and b = 1

 

[gman03]

Let a, b be equal to one maybe?

second that