Which choice is the explicit formula for the following geometric sequence?0.5, -0.1, 0.02, -0.004, 0.0008, ...

1 answer:

6 0

$a_1=0.5\\a_2=-0.1\\a_3=0.02\\a_4=-0.004\\a_5=0.0008\\\\a_n=a_1\cdot q^{n-1}\\\\q=a_2:a_1\to q=-0.1:0.5=-0.2\\\\a_n=0.5\cdot(-0.2)^{n-1}=0.5\cdot(-0,2)^n\cdot(-0.2)^{-1}\\\\=0.5\cdot(-0.2)^n\cdot(-5)=-2.5\cdot(-0.2)^n\\\\\boxed{a_n=-2.5\cdot(-0.2)^n}$

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A 15 ft. telephone pole has a wire that extends from the top of the pole to the ground. The wire and the ground form a 42° angle

Lorico [155]

Answer:

Correct choice is A

Step-by-step explanation:

Consider right triangle ABC formed by the telephone pole (side AB) and ground (side BC). In this triangle AC is the length of the wire, BC is the distance from the base of the pole to the spot where the wire touches the ground and AB=15 ft, ∠ACB=42°.

Then

$\sin 42^{\circ}=\dfrac{AB}{AC}\Rightarrow AC=\dfrac{AB}{\sin 42^{\circ}}=\dfrac{15}{\sin 42^{\circ}}\approx 22.4\ ft.$
$\tan 42^{\circ}=\dfrac{AB}{BC}\Rightarrow BC=\dfrac{AB}{\tan 42^{\circ}}=\dfrac{15}{\sin 42^{\circ}}\approx 16.7\ ft.$