Question

Please answer this right and you'll get brainliest!!

Answer 1

Answer:

Given:

aₙ = - 15 + 5 ( n - 1 ) ...(i)

General Formula for nth term in an AP is:

aₙ = a + d ( n - 1 )  ...(ii)

Comparing (i) and (ii) we can say that,

⇒ a = -15

⇒ d = 5

Now we are required to find the 21st term of the given A.P. Hence we get:

⇒ a₂₁ = a + ( 21 - 1 ) d

⇒ a₂₁ = a + ( 20 ) d

Substituting the information we get:

⇒ a₂₁ = - 15 + 20 ( 5 )

⇒ a₂₁ = - 15 + 100

⇒ a₂₁ = 85

Hence the 21st term of the given A.P. is 85

Answer 2

Given :-

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• $\sf \: a_n$ = - 15 + 5( n - 1 ).. eq. (i)

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To Find :-

• 21st term of this Arithmetic progression

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Formula used :-

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$\color{gold} \bigstar \: \color{teal}\boxed{ \sf \: a_n = a + d(n - 1)}$ Equation (ii)

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Now, when we observe equation (i) and equation (ii), we get to know that,

• a = - 15
• d = 5

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Therefore,

$: \implies \: a_{21} = - 15 + 5(21 - 1) \\ : \implies \: a_{21} = - 15 + 5 \times 20 \: \: \: \: \: \: \\ : \implies \: a_{21} = - 15 + 100 \: \: \: \: \: \: \: \: \: \: \: \: \\ : \implies \: a_{21} = 85 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \:$

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$\color{pink} \sf \therefore \: a_{21} = \boxed{85}$

That is, 21st term of this Arithmetic progression is 85.