I am not quite sure what the question asks for,
But this is what i assume it wants:
Cos A= 0.6489
In this given one, we basically find the size of the angle A
we do cosine inverse on both sides to get the size of the angle A

: It looks like this in the calculator

× cos A=

(0.6489)
(

and cos cancels out)
A=

(0.6489)
A=49.54°
check:
cos 49.54=0.6489 (its right!)
Answer:
The population mean is 5 volts
Step-by-step explanation:
Output voltage is assumed to be normally distributed, with standard deviation 0.25 Volts
s=0.25
n = 8

Sample mean = 
Since n < 30 and population standard deviation is unknown
So, we will use t test
Formula : 

t=-1.69
Refer the t table for p value
Degree of freedom = n-1 = 8-1 = 7
So,
P value >α
So, We are failed to reject null hypothesis
Hence The population mean is 5 volts
The correct answer is D. (3x - 4) (2x + 5)
Here's why:
6x2 + 15x - 8x - 20=
6x2 + 7x - 20
1 meter = 100 centimeters, so 120 centimeters equal to 1.2 meters.
The value is

or

, since it is in the tenths place.