WEBVTT
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The diagram shows a sketch of 𝑦 is equal to cos of 𝑥 degrees for negative 180 is less than or equal to 𝑥 which is less than or equal to 540.
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Part a) Write down the coordinates of 𝐴.
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Remember the graph of 𝑦 is equal to cos of 𝑥 is periodic.
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That means it repeats and it has a period.
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It repeats every 360 degrees.
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This is a useful place to start.
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We know that the cos graph intersects the 𝑦-axis at one.
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It gets back to one at 360 degrees.
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So 360 degrees must be the point on the 𝑥-axis at which the graph reaches one again.
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We can halve this.
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And we now know that the graph reaches negative one at 180.
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Halving again, it intersects the 𝑥-axis at 90 and then 270.
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We add 90 to 360.
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And we can see that it intersects the 𝑥-axis once again at 450 degrees.
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And the graph is also symmetrical in the 𝑦-axis.
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So we can add negative 90 and negative 180.
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Once we have all of that information written down, we can simply read the coordinates for 𝐴 straight from the graph.
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𝐴 has coordinates 180, negative one.
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b) Write down the coordinates of 𝐵.
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We can see that 𝐵 is the point where the graph intersects the 𝑥-axis for the third time.
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The coordinates of 𝐵 are 450, zero.
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The values on the 𝑥-axis represent an angle there in degrees.
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So we can say that the coordinates of 𝐴 are 180 degrees, negative one and the coordinates of 𝐵 are 450 degrees, zero.