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Ksju [112]
3 years ago
11

Find the sum of first 15 terms of an AP whose 4th and 9th t terms are -15 and -30 respectively.

Mathematics
1 answer:
Serga [27]3 years ago
7 0

Answer:

Sum of the first 15 terms = -405

Step-by-step explanation:

a + 3d = -15 (1)

a + 8d = -30 (2)

Where,

a = first term

d = common difference

n = number of terms

Subtract (1) from (1)

8d - 3d = -30 - (-15)

5d = -30 + 15

5d = -15

d = -15/5

= -3

d = -3

Substitute d = -3 into (1)

a + 3d = -15

a + 3(-3) = -15

a - 9 = -15

a = -15 + 9

a = -6

Sum of the first 15 terms

S = n/2[2a + (n − 1) × d]

= 15/2 {2×-6 + (15-1)-3}

= 7.5{-12 + (14)-3}

= 7.5{ -12 - 42}

= 7.5{-54}

= -405

Sum of the first 15 terms = -405

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DanielleElmas [232]

The new player's personal time  is 4.5 seconds.

<h3>What is the new player's personal time?</h3>

The first step is to determine the total time the 5 persons complete the dash.

Total time = 5 x 5.7 = 28.5 seconds

The second step is to determine the total time for the 6 people to complete the dash.

Total time = 6 x 5.5 = 33 seconds

The third step is to find the difference of the time in the previous two steps: 33 - 28.5 = 4.5 seconds

To learn more about mean, please check: brainly.com/question/25842202

6 0
2 years ago
Gretchen rode her snowmobile 1 1/4 miles to a snowmobile trail. She rode on the trail for 5 5/6 miles and then rode back home. W
allsm [11]

Answer:

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Step-by-step explanation:

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5 0
3 years ago
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Help please? 39 points
victus00 [196]
You cannot assume the angles add to 90, but you know since BD is an angle bisector that ABD is equal to DBC, or x-5=2x-6

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3 years ago
How to find y intercept and slope for y=4x-7
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Answer:

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Step-by-step explanation:

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Then, you simplify the right side of the equation.

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