The height, [tex]h[/tex], in feet of the tip of the minute hand of a wall clock as a function of time, [tex]t[/tex], in minutes can be modeled by the equation:

[tex]h = 0.75 \cos \left(\frac{\pi}{30}(t - 15)\right) + 8[/tex]

Which number (from 1 to 12) is the minute hand pointing to at [tex]t = 0[/tex]?

A. 3
B. 6
C. 9
D. 12

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Answer :

To determine the number (from 1 to 12) that the minute hand is pointing to at [tex]\( t = 0 \)[/tex] minutes, we need to understand how the function [tex]\( h=0.75 \cos \left(\frac{\pi}{30}(t-15)\right)+8 \)[/tex] models the height of the tip of the minute hand over time.

1. Evaluate the function at [tex]\( t = 0 \)[/tex]:
[tex]\[ h = 0.75 \cos \left(\frac{\pi}{30}(0-15)\right) + 8 \][/tex]
Simplify inside the cosine term:
[tex]\[ h = 0.75 \cos \left(\frac{\pi}{30} \cdot (-15)\right) + 8 \][/tex]
[tex]\[ h = 0.75 \cos \left(-\frac{15\pi}{30}\right) + 8 \][/tex]
[tex]\[ h = 0.75 \cos \left(-\frac{\pi}{2}\right) + 8 \][/tex]

2. Evaluate the cosine:
[tex]\[ h = 0.75 \cos \left(-\frac{\pi}{2}\right) + 8 \][/tex]
Since [tex]\( \cos \left(-\frac{\pi}{2}\right) = 0 \)[/tex]:
[tex]\[ h = 0.75 \cdot 0 + 8 \][/tex]
[tex]\[ h = 8 \][/tex]

3. Interpreting the height [tex]\( h \)[/tex] in terms of the minute hand position:
- The overall height of the minute hand ranges from 8 (uppermost) to [tex]\( 8 - 0.75 = 7.25 \)[/tex] (lowermost).
- At [tex]\( h = 8 \)[/tex], the minute hand is at the topmost position.

4. Identifying the topmost position on a clock:
- On a standard 12-hour clock, the minute hand points to 12 at the topmost position.

Therefore, at [tex]\( t = 0 \)[/tex] minutes, the minute hand is pointing to:
[tex]\[ \boxed{12} \][/tex]