Find the sum of the geometric series
1+ 0.8 + 0.8^2 + 0.8^3 + ... + 0.8^19

Work Shown:

a = first term = 1

r = 0.8 = common ratio

We know the common ratio is 0.8 because we multiply this common ratio by each term to get the next term. The easiest to spot this is going from term1 to term2. Put another way, term2/term1 = 0.8/1 = 0.8 is our common ratio.

The general form of the nth term of a geometric sequence is and because the last term has an exponent of 19, this means n-1 = 19 solves to n = 20. Therefore, we are summing exactly n = 20 terms here.

Use the formula below to take a shortcut rather than painstakingly find all 20 terms and then summing them.

This value is approximate.

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To check your answer, you could type the following into your calculator

1+0.8+0.8^2+0.8^3+0.8^4+0.8^5+0.8^6+0.8^7+0.8^8+0.8^9+0.8^10+0.8^11+0.8^12+0.8^13+0.8^14+0.8^15+0.8^16+0.8^17+0.8^18+0.8^19

Though as you can see, this is very tedious to type in. This is why the formula in the previous section above is preferred.

the ratio of white tiles to blue tiles is 48: 16. the ratio in it's simplest form is 3: 1.

step-by-step explanation:

ratio: take the first number and add a colon next to it, then add the second number after that. make sure the ratio order matches up with the written problem!

simplest form: we can simplify the ratio 48 : 16 by dividing both terms by the greatest common factor (gcf).

the gcf of 48 and 16 is 16.

divide both terms by 16:

48 ÷ 16 = 3

16 ÷ 16 = 1

reducing to simplest form:

48 : 16 = 3 : 1

point a is the center of the circle that passes through points e, f, and g and the center of the circle that passes through points x, y, and z.