# Pre-Calc

I am really struggling with how to do these problems, I posted them a few minutes ago but the answers/work shown was incorrect.

1)
a) Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number.

cos 12° cos 18° − sin 12° sin 18°

b) And Find its exact value.

2)
a)Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number.

sin 4pi/5 cos 7pi/15 - cos 4pi/5 sin 7pi/15

b) And find its exact value.

3)

Write the trigonometric expression in terms of sine and cosine, and then simplify.

tan θ / cos θ − sec θ

1. 👍 0
2. 👎 0
3. 👁 1,474
1. You must make an effort to memorize the formulas.
(I suggest you memorize the pattern)
cos(A+B) = cosAcosB - sinAsinB
Notice you have that pattern in
cos 12° cos 18° − sin 12° sin 18°
= co(12+18)
= cos 30
which you should have memorized as √3/2 from the 30-6-90 triangle

2) same suggestion, you must know these formulas
sin(A-B) = sinAcosB - cosAsinB
then sin 4pi/5 cos 7pi/15 - cos 4pi/5 sin 7pi/15
= sin(4π/5 - 7π/15)
= sin((1/3)π) or sin π/3 or sin 60°
again you should know that one
sin π/3 = √3/2

3
tanØ/cosØ - secØ
= (sinØ/cosØ) / cosØ - 1/cosØ
= sinØ/cos^2 Ø - cosØ/cos^2 Ø
= (sinØ - cosØ)/cos^2 Ø

1. 👍 0
2. 👎 0

## Similar Questions

1. ### stats

The time, in minutes, it took each of 11 students to complete a puzzle was recorded and is shown in the following list. 9, 17, 20, 21, 27, 29, 30, 31, 32, 35, 58 One of the students who completed the puzzle claimed that there were

2. ### math

The MATHCOUNTS Sprint Round competition consists of 30 problems with a time limit of 40 minutes. Suppose you complete 20 Sprint Round problems in 25 minutes. On average, how many times as long will you be able to spend on each

3. ### science

If the half-life of a 20.0g is known to be 24 minutes, how long will it take for only 5.0 grams of the sample to remain A.6 minutes B.24 minutes C.48 minutes D.96 minutes I NEED HELP!!!!

4. ### statistics

Times for a surgical procedure are normally distributed. There are two methods. Method A has a mean of 28 Minutes and a standard deviation of 4 minutes, while B has a mean of 32 minutes and a standard deviation of 2 minutes.

1. ### Math help

Gold (Au) has a synthetic isotope that is relatively unstable. After 25.5 minutes, a 128-gram sample has decayed to 2 g. What is the half-life of this isotope? 8.5 minutes 2.25 minutes 1.5 minutes 4.25 minutes

2. ### math

In a 3 hour examination of 350 questions, there are 50 mathematics problems. If twice as much time should be allowed for each problem as for each of the other questions, how many minutes should be spent on the mathematical

3. ### Math

Kenneth has 22 math problems to do for homework. He has 12 problems done.How many more problems does he left?if he completes 1 problem every minute,how many more minutes does he have to work?

4. ### math

kenneth has 22 math problems to do for homeworks he has 12 problems done. How many more problems does he have left? If he completes 1 problem every minute, how many more minutes does he have to work?

1. ### Algebra

-Alfonso can write 100 practice problems for the math team in 20 hours, Beauregard can write the same number of problems in 30 hours, and Clyde can write the number of problems in 40 hours. Working together, at what time will the

2. ### Math

In a mixed number or fraction problem, you have dividing and multiplying. Now if you were given a list of multiplying and dividing mixed number and fraction word problems, how can you tell the difference between multipling and

3. ### Math

What is the shortest time it takes to collect a container of water? This is from a Box Plot. The answer choices are: 45 minutes 56 minutes 64 minutes 53 minutes 48 minutes 48 minutes is the lower quartile 56 minutes is the upper

4. ### math

At 8 A.M., Dylan and his neighbor, Mickey, drove in their cars to a city that was 240 miles away from their neighborhood. When Dylan reached the city, Mickey had 40 miles to go. He finally completed the trip 48 minutes later. (a)