the sum of the first 21 term of the progression,-18, -15, -12,
21/2 (2a+20d)
10.5 (2(-18)+20(3))
10.5[-36+60]
10.5×24=252😜😜
a = -18
d = 3
S21 = 21/2 (2a+20d) = ____
To find the sum of the first 21 terms of the arithmetic progression -18, -15, -12..., you can use the formula for the sum of an arithmetic series:
Sn = (n/2) * (a1 + an)
Where Sn represents the sum of the series, a1 is the first term, an is the nth term, and n is the total number of terms.
In this case, a1 = -18 (the first term), an = ? (the 21st term), and n = 21 (the total number of terms).
To find the 21st term (an) of the series, you can use the formula for the nth term of an arithmetic progression:
an = a1 + (n - 1) * d
Where d represents the common difference between consecutive terms of the series.
In this case, a1 = -18 (the first term), n = 21 (the term we want to find), and d = 3 (the common difference between consecutive terms, which can be calculated by subtracting the second term, -15, from the first term, -18).
an = -18 + (21 - 1) * 3
= -18 + 20 * 3
= -18 + 60
= 42
Now that we have found the value of the 21st term (an = 42), we can substitute these values into the formula for the sum of an arithmetic series:
Sn = (n/2) * (a1 + an)
= (21/2) * (-18 + 42)
= (21/2) * 24
= 21 * 12
= 252
Therefore, the sum of the first 21 terms of the given arithmetic progression is 252.
252
The sum of the first 21 terms of the progression
Well, let's see if we can add some humor to math!
To find the sum of the first 21 terms of the progression, we can use the formula for the sum of an arithmetic series. But instead of using boring math, let's bring in some clowns! 🤡🎪
Imagine you have a line of clowns, and each clown has a number on their shirt representing the terms of the progression. The first clown has -18, the second clown has -15, and so on.
Now, let's count all the clowns together while keeping the humor intact!
The first clown says, "-18, negative, but at least it's not positive attitude!"
The second clown chimes in, "-15, you really gotta hand it to me for being a high five with a negative twist!"
As the clowns continue down the line, we keep adding up their numbers and their silly jokes.
So, for the sum of the first 21 terms, we should probably keep a record of all the funny comments those clowns make.