What will be the first negative term in the sequence 87,84,81
1 answer:
Answer:
a₃₁
Step-by-step explanation:
The terms have a common difference between consecutive terms, that is
d = 84 - 87 = 81 - 84 = - 3
This indicates the sequence is arithmetic with nth term
= a₁ + (n - 1)d
where a₁ is the first term and d the common difference
Here a₁ = 87 and d = - 3 , then
= 87 - 3(n - 1) = 87 - 3n + 3 = 90 - 3n
To find when < 0 , solve
90 - 3n < 0 ( subtract 90 from both sides )
- 3n < - 90
Divide both sides by - 3, reversing the symbol as a result of dividing by a negative quantity, then
n > 30
Thus the 31st term will be the first negative term
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To solve this, equate line AB to be equal with line DC.
So,
Line AB = Line DC
(9x-14)in = (3x +4)in
Next group like terms to get the value of x
9x in-3x in = 4in+14in
= 
x = 3in
Since, we now have the value of x, substitute it to line DC’s equation.
DC=(3x+4)in
DC=(3(3) +4)in
DC=(9 +4) in
DC= 13 in
To check if the value is really correct, substitute X to AB
AB=(9x -14)in
AB=(9(3)-14)in
AB=(27-14)in
AB=13 in
To solve this, equate line AB to be equal with line DC.
So,
Line AB = Line DC
(9x-14)in = (3x +4)in
Next group like terms to get the value of x
9x in-3x in = 4in+14in
x = 3in
Since, we now have the value of x, substitute it to line DC’s equation.
DC=(3x+4)in
DC=(3(3) +4)in
DC=(9 +4) in
DC= 13 in
To check if the value is really correct, substitute X to AB
AB=(9x -14)in
AB=(9(3)-14)in
AB=(27-14)in
AB=13 in