Answer:
<h2>
aₙ = 7n - 10</h2>
Step-by-step explanation:
The nth term: 
So:
a₄ = a₁ + 3d
18 = a₁ + 3d ⇒ 3d = 18 - a₁
a₇ = a₁ + 6d
39 = a₁ + 6d
39 = a₁ + 2(18 - a₁)
39 = a₁ + 36 - 2a₁
39 = 36 - a₁
a₁ = -3
3d = 18 - (-3)
3d = 21
d = 7
So the nth term:

By the definition of the hyperbolic function tanh x, we have proven that 
<h3>Hyperbolic functions & Proof of identities </h3>
By definition

Then,















Hence, we have proven that 
Learn more on Proof of Identities here: brainly.com/question/2561079
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Answer:
4 hours
Step-by-step explanation:
it takes thirty minutes to water 1/8 of a lawn, so you will water 2/8 every hour. 8 divided by 2 is 4.