Let $n$ be a positive integer. (a) Prove that \[n^3 = n + 3n(n - 1) + 6 \binom{n}{3}\]by counting the number of ordered triples $(a, b,c)$ of positive integers, where $1 \le a,$ $b,$ $c \le n,$ in two different ways. (b) Prove that \[\binom{n + 2}{3} = (1)(n) + (2)(n - 1) + (3)(n - 2) + \dots + (k)(n - k + 1) + \dots + (n)(1),\]by counting the number of subsets of $\{1, 2, 3, \dots, n + 2\}$ containing three different numbers in two different ways.

Description of the given points can be defined as follows:

Step-by-step explanation:

In points A, If b is less than a and c. so, it calls the smiley face (a, b , c), so we'll have a smiling smile whenever we create a chart! And if b is bigger then a and c, then it should be an angry face, although when we switch the head inside out, they get a grumpy face.    

In point b,  the smirks, which including a greater than b and c, then it is the neutral faces like a is equal to and b equal to c , it can also be seen in certain forms of faces. When the facial is positive, therefore b and b is similar to c. because when we pick a, b and c, but there's a choice of n are neutral.

Its quantity of scowls has been counted. There are many n options to choose a or n-1 forms of picking b. Each value that we can choose for the could also have been the price of b or c. There is also multiplication by 3. Thus 3n(n-1) scowls were present.  

A number of happy face faces we note now. There will be n options for such a then n – 1 options for b, but n – 2 options for c. There were the happy faces of n(n-1)(n-2) = 3C(n,3). There are many grumpy face faces of the configuration of 3C(n,3).  

Thus, n^3 = n + 3n(n – 1)+ 6C(n,3) was its total amount of faces.

(b) We can select two groups of 2 categories one at two numbers to choose three numbers and the other with one group. Its total number of n+2 can be divided into two groups.  

First, there are many two numbers with one group, then n number in another one. This makes up n + 2 number of all. C(2,2) = 1 represents selecting two digits from the two sets. There are many C(n,1) = n forms to select a single organization amount. Which offers us a first 1*n term.

x=17

step-by-step explanation:

solve 3x-24=x+10

then that makes it 2x=34 because you subtract an x from both sides to get rid of the one on the right, and then you add 24 to both sides to get rid of the 24 on the left

divide by both sides by 2 to get your answer so that you can get your answer