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  1. ← All courses
  2. Precalculus
  3. Unit 10: Trigonometric Graphs

Lesson 1 of 3

Sine and cosine models

Describe a repeating pattern with its midline, amplitude, period, and starting point.

Subject to changeOptional future study, outside the current course sequence. This lesson and its homework preview are unassigned and may change.

Lessons and study tools
PracticeKey wordsCalculator

Current units

  1. Unit 1: Essential Review
    1. Find a starting point
    2. Evaluate and compare expressions
    3. Read powers and multiply expressions
    4. Solve equations and describe intervals
    5. Essential algebra review
  2. Unit 2: Functions
    1. Read and use function notation
    2. Combine functions in the right order
    3. Keep inputs and outputs allowed
    4. Describe change and graph behavior
    5. Reverse a function safely
    6. Use symmetry to compare inputs
    7. Functions review
  3. Unit 3: Linear Functions
    1. Build a model with constant change
    2. Write and compare line equations
    3. Reverse a linear model
    4. Build and read piecewise rules
    5. Linear functions review
Optional future study · Subject to change

Unassigned previews outside the current course sequence.

  1. Unit 4: Exponential Functions · Optional future study · Subject to change
    1. Simplify with exponent laws
    2. Interpret rational exponents over the reals
    3. Build repeated-factor models
    4. Solve equations with a common base
    5. Read exponential graphs and their limits
    6. Exponentials review
  2. Unit 5: Quadratics · Optional future study · Subject to change
    1. Factoring patterns
    2. Factoring trinomials
    3. Completing the square
    4. Quadratic models
    5. Linear quadratic systems
    6. Quadratics review
  3. Unit 6: Transformations · Optional future study · Subject to change
    1. Shifts and reflections
    2. Stretches and compressions
    3. Move and reshape a function
    4. Transformations review
  4. Unit 7: Polynomials · Optional future study · Subject to change
    1. Polynomial structure
    2. Polynomial behavior
    3. Polynomial graphs
    4. Polynomials review
  5. Unit 8: Rational Functions · Optional future study · Subject to change
    1. Simplify rational functions safely
    2. Divide polynomials and check remainders
    3. Combine rational expressions
    4. Solve rational equations and check candidates
    5. Rational expressions and equations review
  6. Unit 9: Trigonometry · Optional future study · Subject to change
    1. Right-triangle models
    2. Radians and circular arcs
    3. The unit circle
    4. Trigonometric identities
    5. Linear trigonometric equations
    6. Trigonometry review
  7. Unit 10: Trigonometric Graphs · Optional future study · Subject to change
    1. Current lessonSine and cosine models
    2. Period, frequency, and phase
    3. Build a sine or cosine model
    4. Sine and cosine graphs review
  1. 1Learn it
  2. 2Practice it
  3. 3Homework
  4. 4Finish

Step 1 of 4: Learn it

Learn it · 1 of 8Build the ideaNext: Read the graph and check the equationChoose an activity

One idea at a time. Try the example, then keep going.

Big ideas · 1 of 8

Big ideas

Build the idea

Do this: Read each idea, then say it in your own words.

Key words

  • Key word · Unit 10AmplitudeHalf the distance between a wave’s highest and lowest outputs.Exactly: For y=Asin⁡(B(x−C))+D or y=Acos⁡(B(x−C))+D, amplitude is |A|, with B≠0.Mix-up alert: Amplitude is always nonnegative and is not the vertical shift.See this in Key words
  • Key word · Unit 10MidlineThe horizontal line halfway between a wave’s high and low values.Exactly: For y=Asin⁡(B(x−C))+D or y=Acos⁡(B(x−C))+D, the midline is y=D.Mix-up alert: The midline is an output value, while amplitude measures distance from it.See this in Key words
  1. 1

    1. Amplitude and midline

    A sinusoidal model y=Asin⁡(B(x−h))+D has amplitude |A| and midline y=D. Its range is [D-|A|, D+|A|].

  2. 2

    2. Period and shift

    For a nonconstant curve with A and B not equal to 0, the Key word · Unit 10PeriodThe shortest positive input shift that repeats the whole pattern.Exactly: A fundamental period P>0 satisfies f(x+P)=f(x) wherever defined, with no smaller positive period.Mix-up alert: For a nonconstant transformed sine or cosine, the period is 2π|B|; for tangent it is π|B|.See this in Key words is 2π|B| in radians. The factored form shows the horizontal shift h directly.

    one full repeat
  3. 3

    3. Five helpful points

    Sketch a full cycle at quarter-period intervals. An unreflected cosine starts at a maximum; an unreflected sine starts on its midline, rising when B>0.

  4. 4

    4. Model with units

    A mathematical sine or cosine has all real inputs. A model may restrict time to t≥0 or a stated observation window. State output units and do not assume predictions outside that window are reliable.

Step-through

Read the graph and check the equation

Do this: Follow the labeled graph. Use the four steps to connect its points with the equation.

Model a small wheel whose center is 6 m high and radius is 2 m, starting at its highest point and turning once every 8 s.

Start at 8 mMidline 6 mMinimum 4 mPeriod 8 sh(t) = 6 + 2 cos(πt4)h(t) (meters)02468246810t (seconds)(0,8)(2,6)(4,4)(6,6)(8,8)

Whole picture, 4 steps

4 steps. Tap a number or Show me how it works.

Worked example

Read a transformed curve

Do this: Follow each step on paper before reading the result.

  1. Step 1: Write y=−3sin⁡(2(x−π6))+4.
  2. Step 2: The amplitude is 3 and the midline is y=4.
  3. Step 3: The period is 2π2=π and the shift is π6 right.
  4. Step 4: Sine ranges from -1 to 1, so the output range is [1,7].

Worked example

Build a repeating model

Do this: Follow each step on paper before reading the result.

  1. Step 1: A signal ranges from 5 to 17 units and repeats every 12 s, starting at its maximum.
  2. Step 2: The midline is 17+52=11 and amplitude is 17−52=6.
  3. Step 3: B=2π12=π6.
  4. Step 4: A matching model is s(t)=11+6cos⁡((π6)t),t≥0, in signal units.

Mix-up alert

Common mistake

Do this: Explain the wrong idea and the repair.

Wrong idea: the phase shift of sin⁡(3x−π) is π. Repair: factor the input as 3(x−π3); the shift is π3 right. Divide the whole constant by the input coefficient.

Tip

Do Now · Easy · Paper reference

Do this: Use paper. State the definition before you calculate.

If a sinusoid ranges from 4 to 10, explain why its amplitude is 3 and its midline is 7.

Worked example

Guided practice · Medium · Paper reference

Do this: Work on paper and explain each step before checking it.

For y=5cos⁡(2x)−1:

  1. Step 1: The amplitude is 5.
  2. Step 2: The range is -6 to 4.
  3. Step 3: The period is π.

Watch

Video: Sine and cosine models

Do this: Watch the public lesson, pause to try a step, then return to your practice.

Watch on YouTubeOpens in a new tab. Keep your work here.

Watch for:

  • Reading amplitude, midline and period from the equation.
  • Pause before a worked step and try it on paper. Compare the reasoning, not just the final answer.
Open on YouTube↗ (opens in a new tab)

From The Organic Chemistry Tutor · How To Graph Trigonometric Functions | Trigonometry

The linked video is free to watch. The creator may offer optional paid resources; they are not needed for this lesson. If YouTube is blocked, use the lesson notes and worked examples here.

Step 2 of 4: Practice it

What is left (7 of 7)

Ready when you are.

Activity 1 of 7 · 0 of 7 activities done

Flashcards

Recall and explain

Do this: Say an answer before flipping. Use the hint when needed.

Card 1 of 8

Sine and cosine models

0 Know it0 Still learning

Compare each extreme with the midline.

Deck options
Keyboard help

On the card: Enter or Space flips. Left and Right move. After revealing, 1 marks Still learning and 2 marks Know it. Tab reaches every control.

Question

What is amplitude?

Answer

Half the distance between maximum and minimum output.

Question

What is the midline for a range [2,10]?

Answer

y=6.

Question

What is the amplitude for a range [2,10]?

Answer

4.

Question

What is the period of cos⁡(5x)?

Answer

2π5 radians.

Question

What is the shift of sin⁡(2(x+1))?

Answer

1 unit left.

Question

What is the range of 7−2cos⁡(x)?

Answer

[5,9].

Question

How far apart are quarter-cycle sketch points?

Answer

One fourth of the period.

Question

Does a physical model always allow every real time?

Answer

No. State its time interval and units.

True or false

Test the statements

Do this: Decide true or false, then read why.

Statement 1 of 4

The amplitude of −4cos⁡(x) is -4.

Self-test

Practice set 1

Do this: Work on paper, choose an answer, then read the feedback.

6 questions. One at a time.

Practice, not a grade. No timer. Your best score stays in this browser.

Tip: This is practice, not a grade. Revisit the example for an idea you missed.

Self-test

Practice set 2

Do this: Work on paper, choose an answer, then read the feedback.

6 questions. One at a time.

Practice, not a grade. No timer. Your best score stays in this browser.

Tip: This is practice, not a grade. Revisit the example for an idea you missed.

Write it

Explain your reasoning

Do this: Write a short explanation, then compare it with the model.

Step 1 of 3: Write

Explain why a range of [4,16] and period of 9 s do not determine one unique formula.

0 words · Aim for 20 or more. This is a guide, not a limit.

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Write it

Extra practice · Hard

Do this: Try the extension on paper, then explain your reasoning here.

Step 1 of 3: Write

Can two different sine or cosine equations describe the same graph? Give an example and explain the parameter change.

0 words · Aim for 20 or more. This is a guide, not a limit.

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Match

Match the key words

Do this: Choose a word, then choose its meaning.

Word match round

Connect the ideas

0 / 4 connected

Choose a term, then its meaning. Or drag its grip. Use Tab and Enter or Space; Escape clears.

Terms

Meanings

Step 3 of 4: Homework

Subject to changeOptional preview. This page does not mean this homework is assigned. Only turn it in if your teacher asks.

Optional practice preview · 3 points if assigned

Sine and cosine models practice preview

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Step 4 of 4: Finish

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Next lesson: Period, frequency, and phaseUnit 10: Trigonometric Graphs
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Published with approval from Mr. Farzin Khan Shifat. Last updated October 31, 2026.