Question

a sequence starts a 200 and 30 is subtracted each time 200,170,140 what are the first two numbers in the sequence that are kess then zero

Answer 1

Answer: -10 and -40

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Step-by-step explanation:

a = 200 = first term

d = -30 = common difference

Tn = nth term

Tn = a + d(n-1)

Tn = 200 + (-30)(n-1)

Tn = 200 - 30n + 30

Tn = -30n + 230

Set Tn less than 0 and isolate n

Tn < 0

-30n + 230 < 0

230 < 30n

30n > 230

n > 230/30

n > 7.667 approximately

Rounding up to the nearest whole number gets us
`n \ge 8`

So Tn starts to turn negative when n = 8

We can see that,

Tn = -30n + 230

T7 = -30*7 + 230

T7 = 20

and

Tn = -30n + 230

T8 = -30*8 + 230

T8 = -10 is the 8th term

and lastly

Tn = -30n + 230

T9 = -30*9 + 230

T9 = -40 is the ninth term

Or once you determine that T7 = 20, you subtract 30 from it to get 20-30 = -10 which is the value of T8. Then T9 = -40 because -10-30 = -40.

Answer 2

- 10

- 40

Step-by-step explanation:

By the 7th term you should be pretty close to 0. Let's show that.

a1 = 200

n = 7

d = - 30

t7 = a1 + (n - 1)*d

t7 = 200 + (7 -1)*-30

t7 = 200 + 6*-30

t7 = 200 - 180

t7 = 20

This is the last term that is positive. when you take 30 away from t7 you are going to be in negative territory.

t8 = 200 + (8-1) * - 30

t8 = 200 + 7 * - 30

t8 = 200 - 210

t8 = - 10

Now the 9th term

t9 = 200 + (9 - 1)*-30

t9 = 200 + 8 * - 30

t9 = 200 - 240

t9 = - 40