# mathsWatch

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#1
this formula?
(n+2)(n+1)
n2+3n +2
i am confused 0
16 years ago
#2
(Original post by Mittow)
this formula?
(n+2)(n+1)
n2+3n +2
i am confused Specifically, what confuses you?

You get from the original form to the second form by multiplying out brackets, if that's what you mean...

(n+2)(n+1)
= n^2 + n + 2n + 2
= n^2 + 3n + 2

Elaborate.
0
16 years ago
#3
(Original post by Mittow)
this formula?
(n+2)(n+1)
n2+3n +2
i am confused Did you ever draw rectangles in primary to illustrate multiplication? Thats how to understand how bracket multiplication work.

Take an example:

(2 + 3)(4 + 5)

Draw a rectangle which has one side which is 2cm + 3cm, and mark accurateley where the first two centimeters end and the other three begin. (Actually take yoru time to draw this, it is much easier to see it than to understand a text explaining it). The other side of the rectangle should be 4cm + 5cm centimeters. Now you should have a rectangle measuring 5cm * 9cm.

If you take a closer look at the rectangle you see that it can be divided into 4 small rectangles of dimensions: 2cm * 4cm , 2cm * 5cm, 3cm * 4cm and 3cm * 5cm. Since these rectangles together make up the large rectangle, the sum of their areas must equal the are aof teh huge rectangle. In other words:

(2 + 3)(4 + 5) = 2*4 + 2*5 + 3*4 + 3*5 = 5 * 9 = 45

The same works for letters:

(n+2)(n+1) = n*n + n*1 + 2*n + 2*1 = n^2 + 3n + 2
0
16 years ago
#4
(Original post by Jonatan)
Did you ever draw rectangles in primary to illustrate multiplication? Thats how to understand how bracket multiplication work.

Take an example:

(2 + 3)(4 + 5)

Draw a rectangle which has one side which is 2cm + 3cm, and mark accurateley where the first two centimeters end and the other three begin. (Actually take yoru time to draw this, it is much easier to see it than to understand a text explaining it). The other side of the rectangle should be 4cm + 5cm centimeters. Now you should have a rectangle measuring 5cm * 9cm.

If you take a closer look at the rectangle you see that it can be divided into 4 small rectangles of dimensions: 2cm * 4cm , 2cm * 5cm, 3cm * 4cm and 3cm * 5cm. Since these rectangles together make up the large rectangle, the sum of their areas must equal the are aof teh huge rectangle. In other words:

(2 + 3)(4 + 5) = 2*4 + 2*5 + 3*4 + 3*5 = 5 * 9 = 45

The same works for letters:

(n+2)(n+1) = n*n + n*1 + 2*n + 2*1 = n^2 + 3n + 2
That is one long way of saying (n+2)(n+1) = n(n+1) + 2(n+1) = n^2 + 3n + 2 0
16 years ago
#5
(Original post by theone)
That is one long way of saying (n+2)(n+1) = n(n+1) + 2(n+1) = n^2 + 3n + 2 Well, you assumed that the guy knows hpw bracket ultiplication works, I was trying to explain why...
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