# Urgent urgent maths help

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Please could you explain how to do this:

If the exact value of sin 45= 1/root 2

What is the exact value of sin 135?

Ps this is without a calculator and I think it got something to do with the symmetry of the sin graph....

Thank you so much

If the exact value of sin 45= 1/root 2

What is the exact value of sin 135?

Ps this is without a calculator and I think it got something to do with the symmetry of the sin graph....

Thank you so much

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#2

(Original post by

Please could you explain how to do this:

If the exact value of sin 45= 1/root 2

What is the exact value of sin 135?

Ps this is without a calculator and I think it got something to do with the symmetry of the sin graph....

Thank you so much

**Cherrygrape1234**)Please could you explain how to do this:

If the exact value of sin 45= 1/root 2

What is the exact value of sin 135?

Ps this is without a calculator and I think it got something to do with the symmetry of the sin graph....

Thank you so much

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#3

**Cherrygrape1234**)

Please could you explain how to do this:

If the exact value of sin 45= 1/root 2

What is the exact value of sin 135?

Ps this is without a calculator and I think it got something to do with the symmetry of the sin graph....

Thank you so much

then plot the known value and it should be obvious...

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(Original post by

Your thought is correct! Do you know how to draw the graph? Do you know how sin (180 - x) relates to sin x?

**davros**)Your thought is correct! Do you know how to draw the graph? Do you know how sin (180 - x) relates to sin x?

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(Original post by

Draw the graph for Y = Sin X in the interval 0 to 180.

then plot the known value and it should be obvious...

**mnot**)Draw the graph for Y = Sin X in the interval 0 to 180.

then plot the known value and it should be obvious...

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#6

(Original post by

Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

**Cherrygrape1234**)Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

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#7

(Original post by

Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

**Cherrygrape1234**)Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

Also, you should know the formula for sin(A - B) which should in turn tell you what sin(180 - x) is equal to in terms of sin x.

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#8

(Original post by

Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

**Cherrygrape1234**)Yeah so if I plot sin 45 how do I get sin 135 from it? 🤔

At both x = 0 & x = 180, y = 0. And this is obvious looking at the graph. At every point in this region (bar x = 90) for every value of y their are 2 solutions for x.

Now draw out the curve, plot the result for x = 45 and look at the relationship x at 135 has.

Last edited by mnot; 3 weeks ago

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(Original post by

Hint: the graph of y = sin(x°) has a line of reflection symmetry at x = 90.

**MarkFromWales**)Hint: the graph of y = sin(x°) has a line of reflection symmetry at x = 90.

Or sin 180 - sin 45?

Last edited by Cherrygrape1234; 3 weeks ago

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(Original post by

Are you working at A level? If you know the graph, the symmetry should make it obvious.

Also, you should know the formula for sin(A - B) which should in turn tell you what sin(180 - x) is equal to in terms of sin x.

**davros**)Are you working at A level? If you know the graph, the symmetry should make it obvious.

Also, you should know the formula for sin(A - B) which should in turn tell you what sin(180 - x) is equal to in terms of sin x.

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(Original post by

Lets imagine the curve y = Sin(x) in the region x=0 to x=180.

At both x = 0 & x = 180, y = 0. And this is obvious looking at the graph. At every point in this region (bar x = 90) for every value of y their are 2 solutions for x.

Now draw out the curve, plot the result for x = 45 and look at the relationship x at 135 has.

**mnot**)Lets imagine the curve y = Sin(x) in the region x=0 to x=180.

At both x = 0 & x = 180, y = 0. And this is obvious looking at the graph. At every point in this region (bar x = 90) for every value of y their are 2 solutions for x.

Now draw out the curve, plot the result for x = 45 and look at the relationship x at 135 has.

I kinda get it now!

But which one?

You either do sin 45 + sin 90

Or sin 180 - sin 45?

Last edited by Cherrygrape1234; 3 weeks ago

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#12

(Original post by

Ohhhh

I kinda get it now!

You either do sin 45 + sin 90

Or sin 180 - sin 45?

**Cherrygrape1234**)Ohhhh

I kinda get it now!

You either do sin 45 + sin 90

Or sin 180 - sin 45?

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(Original post by

No, it's simpler than that. If you make a rough sketch of the graph of y = sin(x°) between x = 0 and x = 180 and mark in the line of symmetry you should just see the answer. (Going into your exam you will need to know the graphs of sine and cosine so you can sketch them instantly).

**MarkFromWales**)No, it's simpler than that. If you make a rough sketch of the graph of y = sin(x°) between x = 0 and x = 180 and mark in the line of symmetry you should just see the answer. (Going into your exam you will need to know the graphs of sine and cosine so you can sketch them instantly).

I did the symmetry and it is sin 90 = 1

Then how do I get the answer?

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#15

(Original post by

Umm I still don’t 😂

I did the symmetry and it is sin 90 = 1

Then how do I get the answer?

**Cherrygrape1234**)Umm I still don’t 😂

I did the symmetry and it is sin 90 = 1

Then how do I get the answer?

Note: the red lines are mirror images of each other.

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So the answer is 1/root 2 as well

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#17

(Original post by

Thank you so much I finally understand!!

So the answer is 1/root 2 as well

**Cherrygrape1234**)Thank you so much I finally understand!!

So the answer is 1/root 2 as well

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