# Trigonometric ratios help please? Watch

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A trigonometric function of a number is given below. Without calculator, find all the other numbers x, 0 ≤ x ≤ 360, such that the same function of x is equal to the given trigonometric ratio. E.g. if you're given sin 80°, then x = 100°, since sin 100° = sin 80°

g) sin 400°

h) cos(-30°)

j) sin(-260°)

k) cos(-200°)

g) sin 400°

h) cos(-30°)

j) sin(-260°)

k) cos(-200°)

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#2

draw a sine graph fairly accurately.

find sin 400° on your graph. draw a horizontal line y = sin 400°

see where it cuts the sine graph between 0° and 360°; relate the x values to the 400° , taking into account symmetry and periodicity.

repeat with cosine graph etc

find sin 400° on your graph. draw a horizontal line y = sin 400°

see where it cuts the sine graph between 0° and 360°; relate the x values to the 400° , taking into account symmetry and periodicity.

repeat with cosine graph etc

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#3

(Original post by

A trigonometric function of a number is given below. Without calculator, find all the other numbers x, 0 ≤ x ≤ 360, such that the same function of x is equal to the given trigonometric ratio. E.g. if you're given sin 80°, then x = 100°, since sin 100° = sin 80°

g) sin 400°

h) cos(-30°)

j) sin(-260°)

k) cos(-200°)

**osayuki**)A trigonometric function of a number is given below. Without calculator, find all the other numbers x, 0 ≤ x ≤ 360, such that the same function of x is equal to the given trigonometric ratio. E.g. if you're given sin 80°, then x = 100°, since sin 100° = sin 80°

g) sin 400°

h) cos(-30°)

j) sin(-260°)

k) cos(-200°)

Would you know cos and sin of 0, 30, 45, 60, 90...?

EDIT: Yikes, I didn't read the question properly.

You can use a graph, or a CAST circle, or some formulas.

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(Original post by

draw a sine graph fairly accurately.

find sin 400° on your graph. draw a horizontal line y = sin 400°

see where it cuts the sine graph between 0° and 360°; relate the x values to the 400° , taking into account symmetry and periodicity.

repeat with cosine graph etc

**the bear**)draw a sine graph fairly accurately.

find sin 400° on your graph. draw a horizontal line y = sin 400°

see where it cuts the sine graph between 0° and 360°; relate the x values to the 400° , taking into account symmetry and periodicity.

repeat with cosine graph etc

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(Original post by

Are you familiar with the 'special triangles'?

Would you know cos and sin of 0, 30, 45, 60, 90...?

EDIT: Yikes, I didn't read the question properly.

You can use a graph, or a CAST circle, or some formulas.

**EricPiphany**)Are you familiar with the 'special triangles'?

Would you know cos and sin of 0, 30, 45, 60, 90...?

EDIT: Yikes, I didn't read the question properly.

You can use a graph, or a CAST circle, or some formulas.

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#6

(Original post by

Thank you, how do I use the CAST circle if the value is negative e.g. sin(-260)?

**osayuki**)Thank you, how do I use the CAST circle if the value is negative e.g. sin(-260)?

Two ways I can think of doing this:

Either, find the angle 260 and then reflect in the x-axis.

Or, add 360 to the angle until it is positive, -260 + 360 = 100 so find the angle 100. (360 degrees is one full turn, so it brings you back to the same place).

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(Original post by

Technically you just measure the angle in the opposite direction.

Two ways I can think of doing this:

Either, find the angle 260 and then reflect in the x-axis.

Or, add 360 to the angle until it is positive, -260 + 360 = 100 so find the angle 100. (360 degrees is one full turn, so it brings you back to the same place).

**EricPiphany**)Technically you just measure the angle in the opposite direction.

Two ways I can think of doing this:

Either, find the angle 260 and then reflect in the x-axis.

Or, add 360 to the angle until it is positive, -260 + 360 = 100 so find the angle 100. (360 degrees is one full turn, so it brings you back to the same place).

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#8

Just visualise or draw the graph and u can see that sin400 is the same value as sin40 and sin140. Do the same for the others

Posted from TSR Mobile

Posted from TSR Mobile

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(Original post by

Just visualise or draw the graph and u can see that sin400 is the same value as sin40 and sin140. Do the same for the others

Posted from TSR Mobile

**eternaforest**)Just visualise or draw the graph and u can see that sin400 is the same value as sin40 and sin140. Do the same for the others

Posted from TSR Mobile

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#11

Use CAST!

For a value larger than 360, keep adding to it until you get 400. Then whatever you added is your related angle.

For the negative angle instead of going anti-clockwise, go clockwise.

For a value larger than 360, keep adding to it until you get 400. Then whatever you added is your related angle.

For the negative angle instead of going anti-clockwise, go clockwise.

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#12

(Original post by

Thank you

**osayuki**)Thank you

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