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Algebraic Proof help

11 replies

Wiltinglillies · 20/07/2020 13:16

I am supposed to be helping with this. I can do (c), but totally stumped by questions (a) and (b). If I simplify the left side of (a) I just get 24, and for (b) I get -10.
Help!!!!

Algebraic Proof help
OP posts:
Lougle · 20/07/2020 13:22

Let n be 1.

LHS: (1+5)² -(1+1)² = 36-4=32
RHS: 8(1+3)= 8×4=32

Same process for b

CatherinedeBourgh · 20/07/2020 13:24

Are you remembering to multiply out the second term inside brackets, si the minus applies to all of it?

CatherinedeBourgh · 20/07/2020 13:26

I’m not sure showing that it works if n=1 constitutes proof

10brokengreenbottles · 20/07/2020 13:26

For a

(n+5)(n+5) - (n+1)(n+1) = 8n + 24

(n2 + 10n + 25) - (n2 + 2n + 1) = 8n + 24

8n + 24 = 8n + 24

Quarantino · 20/07/2020 13:27

Can you photo the whole question?
Lougle's example only shows that that works for n=1 - are you meant to prove it more completely for all values of x?

Lougle · 20/07/2020 13:28

The other way to do it is:

(n+5)²=n²+10n+25 (a)
(n+1)²=n²+2n+1 (b)

a-b is 8n +24 which is the same as 8(n+3)

10brokengreenbottles · 20/07/2020 13:28

Slow at posting, I agree with Catherine, are you forgetting to (n+5)^2 is actually (n+5)(n+5)?

Quarantino · 20/07/2020 13:28

Or what 10broken said!

Svalberg · 20/07/2020 13:29

You don't need to find a value for n. Just expand the brackets on both sides. So for a) you get:
LHS
n2+10n+25-(n2+2n+1)
Which is
n2+10n+25-n2-2n-1
Which simplifies to
8n+24

RHS
8n+8×3
is
8n+24

So the LHS is identical to the RHS

cakeandcustard · 20/07/2020 13:37

Multiply out the brackets on the left hand side

Collect together like terms

Factorise to make it look like the right

Wiltinglillies · 20/07/2020 14:24

are you forgetting to (n+5)^2 is actually (n+5)(n+5)?
BlushYESBlush
Thank you!!!

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