Mary Jane Sterling - Pre-Calculus - 1001 Practice Problems For Dummies (+ Free Online Practice)

386. A normal conversation is 60 decibels (dB). What is the intensity of the sound of the conversation (in watts per square meter)? Use the following formula, where L is decibels and I is the intensity of the sound: .

387. Two earthquakes occurred in different parts of the country. The first earthquake had a magnitude of 8.0, and the second had a magnitude of 4.0. Compare the intensity of the earthquakes using the equation , where M is the magnitude, I is the intensity measured from the epicenter, and I 0is a constant.

388. A town had a population of 6,250 in 1975 and a population of 8,125 in 2010. If the rate of growth is exponential, what will the population be in 2040? Use the exponential model , where y is the resulting population, C is the initial amount, k is the growth or decay rate, and t is the time in years.

389. In 2000, a house was appraised at $179,900. In 2013, it was reappraised at $138,000. If the decline rate is exponential, what will the value of the house be in 2020? Round the value to the nearest dollar. Use the exponential model , where y is the resulting value, C is the initial amount, k is the growth or decay rate, and t is the time in years.

390. One student with a contagious flu virus goes to school when they’re sick. The school district includes 7,500 students and 1,000 staff members. The growth of the virus is modeled by the following equation, where y is the number infected and t is time in days: . When 45% of the students and staff members fall ill, the schools will close. How many days before the schools are closed? Round to the nearest whole day.

Chapter 7

Trigonometric functions are special in several ways. The first characteristic that separates them from all the other types of functions is that input values are always angle measures. You input an angle measure, and the output is some real number. The angle measures can be in degrees or radians — a degree being one-360th of a slice of a circle, and a radian being about one-sixth of a circle. Each type has its place and use in the study of trigonometry.

Another special feature of trig functions is their periodicity; the function values repeat over and over and over, infinitely. This predictability works well with many types of physical phenomena, so trigonometric functions serve as models for many naturally occurring observations.

In this chapter, you’ll work with trigonometric functions and their properties in the following ways:

Defining the basic trig functions using the sides of a right triangle

Expanding the input values of trig functions by using the unit circle

Exploring the right triangle and trig functions to solve practical problems

Working with special right triangles and their unique ratios

Changing angle measures from degrees to radians and vice versa

Determining arc length of pieces of circles

Using inverse trig functions to solve for angle measures

Solving equations involving trig functions

Don’t let common mistakes trip you up; keep in mind that when working with trigonometric functions, some challenges will include the following:

Setting up ratios for the basic trig functions correctly

Recognizing the corresponding sides of right triangles when doing applications

Remembering the counterclockwise rotation in the standard position of angles

Measuring from the terminal side to the x -axis when determining reference angles

Keeping the trig functions and their inverses straight from the functions and their reciprocals

391−396Use the triangle to find the trig ratio.

391.

Illustration by Thomson Digital

392.

Illustration by Thomson Digital

393.

Illustration by Thomson Digital

394.

Illustration by Thomson Digital

395.

Illustration by Thomson Digital

396.

Illustration by Thomson Digital

397−406Solve the problem. Round your answer to the nearest tenth unless otherwise indicated.

397. A ladder leaning against a house makes an angle of 30° with the ground. The foot of the ladder is 7 feet from the foot of the house. How long is the ladder?

398. A child flying a kite lets out 300 feet of string, which makes an angle of 35° with the ground. Assuming that the string is straight, how high above the ground is the kite?

399. An airplane climbs at an angle of 9° with the ground. Find the ground distance it has traveled when it reaches an altitude of 400 feet.

400. A car is traveling up a grade with an angle of elevation of 4°. After traveling 1 mile, what is the vertical change in feet?

401. Jase is in a hot air balloon that is 600 feet above the ground, where they can see their brother Willie. The angle of depression from Jase’s line of sight to Willie is 25°. How far is Willie from the point on the ground directly below the hot air balloon?

402. A bird is flying at a height of 36 feet and spots a windowsill 8 feet off the ground on which to perch. If the windowsill is at a 28° angle of depression from the bird, how far must the bird fly before it can land?