Practice Problem (Intro to Discrete Math Class)

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• Jan 15th 2009, 08:32 AM
Edbaseball17
Practice Problem (Intro to Discrete Math Class)
Hey Everyone,

Just so you know I am in an Intro to Discrete Math class so this stuff should be pretty simple to the rest of you, but I'm not very good at it. This is an example question that is up to me if i want to do it or not, the professor does not care. Any help would be appreciated.

Given that \$\displaystyle A_n=5n+3\$ for any \$\displaystyle n>=1\$, is it true that \$\displaystyle A_n=5*A_{(n-1)} -3\$?
• Jan 15th 2009, 08:37 AM
HallsofIvy
Quote:

Originally Posted by Edbaseball17
Hey Everyone,

Just so you know I am in an Intro to Discrete Math class so this stuff should be pretty simple to the rest of you, but I'm not very good at it. This is an example question that is up to me if i want to do it or not, the professor does not care. Any help would be appreciated.

Given that \$\displaystyle A_n=5n+3\$ for any \$\displaystyle n>=1\$, is it true that \$\displaystyle A_n=5*A_(n-1) -3\$?

I'm new to this so not sure how to make (n-1) all subscript, but it should be.

To make all of some expression a subscript enclose it in { }.
To calculate that, think of \$\displaystyle A_n\$ as a function A(n).
If \$\displaystyle A_n= 5n+3\$, then \$\displaystyle A_{n-1}= 5(n-1)+ 3= 5n- 2\$.
Put 5n+3 in place of \$\displaystyle A_n\$ and 5n- 2 in place of \$\displaystyle A_{n-1}\$ in that expression and see if it is true.
Is 5n+3= 5(5n-2)-3?
• Jan 15th 2009, 09:38 AM
Edbaseball17
Quote:

Originally Posted by HallsofIvy
To make all of some expression a subscript enclose it in { }.
To calculate that, think of \$\displaystyle A_n\$ as a function A(n).
If \$\displaystyle A_n= 5n+3\$, then \$\displaystyle A_{n-1}= 5(n-1)+ 3= 5n- 2\$.
Put 5n+3 in place of \$\displaystyle A_n\$ and 5n- 2 in place of \$\displaystyle A_{n-1}\$ in that expression and see if it is true.
Is 5n+3= 5(5n-2)-3?

ok so here is what I cam up with:

5n+3 = 5(n-2)-3 = 25n-10-3 = 25n-7

so the answer is false.

is this correct?