10 is the base. If you get stuck on anymore problems like this you can tell which one is the base by looking where the exponent is in the problem. Hope this helps!!

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9² = 12² + 15² - 2 (12) (15) cos (B)
81 = 144 + 225 - 360 cos(B)
81 = 369 - 360 cos (B)
360 cos (B) = 369 - 81
360 cos (B) = 288
cos (B) = 0.8
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Answer: Cosine B = 0.8
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12² = 15² + 9² - 2 (15)(9) cos (A)
144 = 225 + 81 - 270 Cos A
144 = 306 - 270 Cos A
270 Cos A = 162
Cos A = 3/5 or 0.6
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Answer: Cosine Angle A = 3/5
Yeah his answer is correct Good job!
Answer:
107.50
Step-by-step explanation:
Given the following :
Midpoint (S)____F
S y 93 95 97 99 101 103 105 107 109 111 f 19 25 38 17 12 10 5 4 4 2
Calculating the mean and standard deviation using a calculator :
The mean(m) of the data above = 98.12
Standard deviation (sd) = 4.02
Proportion = 99% of population
From z table = 2.33
Using :
Zscore =(x - m) / sd
2.33 = (x - 98.12) / 4.02
2.33 * 4.02 = x - 98.12
9.3666 = x - 98.12
9.3666 + 98.12= x
x = 107.4866
X = 107.50