Ineed to know how to simplify using conjugate

Solve 2 - 3 cos x = 5 + 3 cos x for 0° ≤ x ≤ 180° a. 150° b. 30° c. 60° d. 120°

What are the solutions of the equation x4 + 6x2 + 5 = 0? use u substitution to solve.

1) a researcher is studying a population of bats in which 16% of the population has a certain trait. the researcher wants sampling distribution with a standard deviation that is less than 2%. which sample sizes could the researcher use? select all that apply : a)n=200 b) n=300 c) n=400 d) n=500 2) from a normal distribution population, a simple random sample of size 38 is taken. the mean of the sample is 82 and the standard deviation of the sample is 4. what is the 90% confidence interval for the population mean? round to the nearest tenth ( [1], 83.1)