Answer:
To find the critical value \( z_{c} \) for a given level of confidence \( c \), we need to look up the area between the critical values in the standard normal distribution table or use technology.
Since the area in each tail is \( \frac{1 - c}{2} \), we can find the area to the left of the critical value, which is \( \frac{1 - c}{2} + c \). We then look up this area in the standard normal distribution table or use technology to find the corresponding \( z \)-score.
For example, if \( c = 0.95 \) (which corresponds to a 95% confidence level), then the area to the left of the critical value is \( \frac{1 - 0.95}{2} + 0.95 = 0.975 \). Looking up the \( z \)-score corresponding to an area of 0.975 in the standard normal distribution table or using technology, we find the critical value \( z_{c} \).