Answer: 21
Step-by-step explanation: To solve this problem, we can first set up a proportion because we know that 3 is to 7 as 9 is to x.
So we have
.
Now, we can use cross products to find the missing value.
So we have 3 time x which is 3x and 7 times 9 which is 63.
Rewriting our equation, we have 3x = 63.
Dividing both sides by 3, we find that <em>x = 21</em>.
So, <em>x = 21</em>.
The red arrows in the middle mean that they are parallel so the slopes are the same.
A(n)=4+4(n-1)
a(n)=4+4n-4
a(n)=4n
76=4n
n=19
The sum of any arithmetic sequence (series are infinite) is:
(a+a(n))(n/2)
The average of the first and last terms times the number of terms, in this case we found that n=19 so:
19(4+76)/2=760