New
New
Year 11
Higher

Interpreting the trigonometric graphs

I can read values from the graphs and can identify how many solutions exist within a given range.

New
New
Year 11
Higher

Interpreting the trigonometric graphs

I can read values from the graphs and can identify how many solutions exist within a given range.

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Lesson details

Key learning points

  1. Reading solutions from trigonometric graphs is the same as reading solutions from any other graph
  2. Due to the period, there may be more than one solution
  3. It is possible to predict the number of solutions that exist within a given range

Keywords

  • Trigonometric functions - Trigonometric functions are commonly defined as ratios of two sides of a right-angled triangle for a given angle.

  • Sine function - The sine of an angle (sin(θ°)) is the y-coordinate of point P on the triangle formed inside the unit circle.

  • Cosine function - The cosine of an angle (cos(θ°)) is the x-coordinate of point P on the triangle formed inside the unit circle.

  • Tangent function - The tangent of an angle (tan(θ°)) is the y-coordinate of point Q on the triangle which extends from the unit circle.

  • Period (of a function) - For a repeating function, the period is the distance of one repetition of the entire function.

Common misconception

Pupils assume that the graph displayed always shows the number of solutions.

It is important to compare the range of values that the graph is displaying against what is being defined in the question.

If you wish to provide additional challenge, consider taking away the graphs so that pupils must either sketch the graphs themselves or use the unit circle to determine the number of solutions.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
For a repeating function, the __________ is the distance of one repetition of the entire function.
tangent
circle
Correct answer: period
sine
cosine
Q2.
Match the equivalent values.
Correct Answer:$$\tan(20°)$$,0.364 (3 s.f)

0.364 (3 s.f)

Correct Answer:$$\tan(80°)$$,5.67 (3 s.f)

5.67 (3 s.f)

Correct Answer:$$\tan(97°)$$,-8.14 (3 s.f)

-8.14 (3 s.f)

Correct Answer:$$\tan(105°)$$,-3.73 (3 s.f)

-3.73 (3 s.f)

Q3.
Considering the cosine graph, what is the interval range showing a period?
$$ 0°\leq x \leq 90° $$ 
Correct answer: $$ 0°\leq x \leq 360° $$ 
$$ 0°\leq x \leq 180° $$ 
$$ 0°\leq x \leq 720° $$ 
Q4.
Match the values of $$x$$ to the values of $$y$$ given $$y=x^2$$.
Correct Answer:$$x = 5$$,$$y = 25$$

$$y = 25$$

Correct Answer:$$x = 2$$,$$y = 4$$

$$y = 4$$

Correct Answer:$$x = -3$$,$$y = 9$$

$$y = 9$$

Correct Answer:$$x = 8$$,$$y = 64$$

$$y = 64$$

Correct Answer:$$x = -6$$,$$y = 36$$

$$y = 36$$

Q5.
Using the function $$y=x^2$$, explain how you can show $$x = 3$$ and $$x = -3$$ give the same value of $$y$$.
Correct answer: Substitute the value for $$x$$ into $$y=x^2$$ and both will give 9.
Correct answer: Using inverse functions we know $$ \pm\sqrt{y} = x$$ gives $$x = \pm3$$.
Correct answer: Use Desmos to see when $$ y = 9$$, $$x = \pm3$$.
There is only one value of $$x$$ which maps to $$y$$ because only $$3^2 =9$$.
There is only one value of $$x$$ as all $$x$$ values must be positive.
Q6.
Using the tangent graph, what is the interval range showing a period?
$$ 0°\leq x \leq 90° $$ 
$$ 0°\leq x \leq 360° $$ 
Correct answer: $$ 0°\leq x \leq 180° $$ 
$$ 0°\leq x \leq 720° $$ 

6 Questions

Q1.
Using the sine graph, what is the interval range showing a period?
$$ 0°\leq x \leq 90° $$ 
Correct answer: $$ 0°\leq x \leq 360° $$ 
$$ 0°\leq x \leq 180° $$ 
$$ 0°\leq x \leq 720° $$ 
Q2.
Using Desmos, draw a cosine graph with the $$x$$ axis interval of $$ 0°\leq x \leq 360° $$ and solve for $$\cos(x°) = 1$$.
Correct answer:
90°
180°
270°
Correct answer: 360°
Q3.
Using Desmos, draw a sine graph with the $$x$$ axis interval of $$ 0°\leq x \leq 360° $$ and solve for $$\sin(x°) = 1$$.
45°
Correct answer: 90°
180°
360°
Q4.
Using Desmos, draw a sine graph with the $$x$$ axis interval of $$ 0°\leq x \leq 360° $$ and estimate the solutions for $$\sin(x) = 0.65$$.
Correct answer: 41°
Correct answer: 139°
141°
49°
21°
Q5.
How can you check that the solutions to $$y=\cos(x°) = 0.42$$ within the interval of $$ 0°\leq x \leq 720° $$ are correct?
Correct answer: Substitute the value for $$x$$ into $$y=\cos(x°)$$ and they will give 0.42...
Using inverse functions we know $$ \arctan(0.42)$$ will give the only answer.
Correct answer: Use Desmos and draw $$y=0.42$$ and $$y=\cos(x°)$$ and find the intersections.
There are an infinite number of solutions.
Q6.
How many solutions will there be when $$\tan(x) = 1.6$$ in the interval $$ 0°\leq x \leq 360° $$?
Correct Answer: 2, two