What is the sum of the arithmetic sequence 3, 9, 15..., if there are 26 terms?

2 answers:

7 0

9 - 3 = 6, 15-9 = 6 the difference is 6, So d = 6

First term: a1 = 3

Sn = n*(a1 + an)/2

Sn = n*(a1 + a1 + (n-1)*d)/2

Sn = n*(2*a1 + (n-1)*d)/2

substitute 26 for n
 S26 = 26*(2*a1 + (26-1)*d)/2

substitute 3 for a1

S26 = 26*(2*3 + (26-1)*d)/2

substitute 6 for d

S26 = 26*(2*3 + (26-1)*6)/2 

S26 = 2,028

marissa [1.9K]4 years ago

3 0

Sum of an arithmetic series is:

S = n*(a_1+a_n)/2, that easy.

n is the number of terms, 26 in your case. a_n is a_26. We need to find the series!

a_n = a_1 + (n-1)*d, the difference, d, is 6.

So a_n = 3 + (n-1)*6 = 6*n-3 (check it works: 3, 9, 15, ...)

Now a_26 = 6*26-3 = 153, so finally:

S = 26*(3+153)/2 = 26*78 = 2028

2028 is the answer

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In triangle ABC above, AD is perpendicular to CB. If the lengths of AD and CB were both increased by 50%, how would the area of

astra-53 [7]

Answer:

The answer is below

Step-by-step explanation:

A triangle is a polygon with three sides and three angles. There are different types of triangles such as scalene triangle, equilateral triangle, isosceles triangle.

The area of a triangle is given as:

A = (1/2) * b * h

where b = base of triangle, h = height of triangle , A = area

Let BC = base = x, and AD = height = y, hence:

A = (1/2) * x * y = 0.5xy

If the lengths of AD and CB were both increased by 50%, hence:

new AD = y + 0.5y = 1.5y, new CB = x + 0.5x = 1.5x

The new area= (1/2) * 1.5y * 1.5x = 1.125xy

Increased area / area = 1.125xy / 0.5xy = 2.25

If the lengths are increased by 50%, the area would also increase and the new area would be 2.25 times