# Higher maths problem

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Rox17

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#1

You have to solve for cosTPQ. Idk what to do, I did cosTPQ=cos(2x + 90) and did the expansion but I got a negative number? Please helppp

https://ibb.co/s58fHt4

https://ibb.co/s58fHt4

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mqb2766

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#2

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#2

(Original post by

You have to solve for cosTPQ. Idk what to do, I did cosTPQ=cos(2x + 90) and did the expansion but I got a negative number? Please helppp

https://ibb.co/s58fHt4

**Rox17**)You have to solve for cosTPQ. Idk what to do, I did cosTPQ=cos(2x + 90) and did the expansion but I got a negative number? Please helppp

https://ibb.co/s58fHt4

Assuming the diagram is correct and Im understanding the original problem, why not just calculate x, then use it to get the actual angle you want.

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Rox17

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#3

I can't get you the original question bc it's in a textbook and I don't have it with me. I also should've mentioned that this is non calculator

https://ibb.co/XsDqcrV

https://ibb.co/XsDqcrV

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mqb2766

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#4

(Original post by

I can't get you the original question bc it's in a textbook and I don't have it with me. I also should've mentioned that this is non calculator

https://ibb.co/XsDqcrV

**Rox17**)I can't get you the original question bc it's in a textbook and I don't have it with me. I also should've mentioned that this is non calculator

https://ibb.co/XsDqcrV

Note that as its > 90, youd expect cos() to be negative. However, you seem to double the trig value rather than doubling the angle, then taking the trig of that.

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Rox17

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#5

How do I double just the angle? I think I'm supposed to calculate the exact value, not the actual angle. I did cos90=0 since I took the 90 from the right angle at the top

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mqb2766

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#6

(Original post by

How do I double just the angle? I think I'm supposed to calculate the exact value, not the actual angle. I did cos90=0 since I took the 90 from the right angle at the top

**Rox17**)How do I double just the angle? I think I'm supposed to calculate the exact value, not the actual angle. I did cos90=0 since I took the 90 from the right angle at the top

Last edited by mqb2766; 1 month ago

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#7

Naan102

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#8

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#9

No I didnt😭😭it's something to do w that cos90 i think bc it makes the answer negative, ill ask my teacher od Wednesday if I still can't figure it out

Last edited by Rox17; 1 month ago

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#10

(Original post by

No I didnt😭😭it's something to do w that cos90 i think bc it makes the answer negative, ill ask my teacher od Wednesday if I still can't figure it out

**Rox17**)No I didnt😭😭it's something to do w that cos90 i think bc it makes the answer negative, ill ask my teacher od Wednesday if I still can't figure it out

Have you written the identity out clearly for cos(2x + 90)? I.e. try getting the sin(2x) part correct.

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#11

(Original post by

As above, why do you think that cos(2x+90) being negative is wrong?

Have you written the identity out clearly for cos(2x + 90)? I.e. try getting the sin(2x) part correct.

**mqb2766**)As above, why do you think that cos(2x+90) being negative is wrong?

Have you written the identity out clearly for cos(2x + 90)? I.e. try getting the sin(2x) part correct.

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#12

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#12

(Original post by

Bc it's a triangle and I'm pretty sure it can't be a negative angle right? I've rewritten it with the correct 2x part but the cos90 makes the first part 0 so the second part becomes negative? Or am I being stupid😭

**Rox17**)Bc it's a triangle and I'm pretty sure it can't be a negative angle right? I've rewritten it with the correct 2x part but the cos90 makes the first part 0 so the second part becomes negative? Or am I being stupid😭

In your identity, the cos(90) is indeed 0, so the value of cos(2x+90) is determined by the second part.

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#13

(Original post by

sin(x) and/or cos(x) is certainly not negative. But the angle is 2x + 90, so what must the sign of cos(2x + 90) be?

In your identity, the cos(90) is indeed 0, so the value of cos(2x+90) is determined by the second part.

**mqb2766**)sin(x) and/or cos(x) is certainly not negative. But the angle is 2x + 90, so what must the sign of cos(2x + 90) be?

In your identity, the cos(90) is indeed 0, so the value of cos(2x+90) is determined by the second part.

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#14

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#14

(Original post by

But the second part is taken away from the first part and there's no negatives in it so it's always gonna be negative?

**Rox17**)But the second part is taken away from the first part and there's no negatives in it so it's always gonna be negative?

so cos(2x+90) is indeed negative.

https://sites.google.com/view/tlmath...e3-trig-graphs

If you don't have your textbook handy where the question comes from, its really worth waiting until you do have it to go over the bits properly rather than being led too much to the answer.

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Naan102

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#15

**Rox17**)

No I didnt😭😭it's something to do w that cos90 i think bc it makes the answer negative, ill ask my teacher od Wednesday if I still can't figure it out

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#16

(Original post by

Can u post the question when u have it. Thanks

**Naan102**)Can u post the question when u have it. Thanks

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#17

(Original post by

2x+90 > 90

so cos(2x+90) is indeed negative.

https://sites.google.com/view/tlmath...e3-trig-graphs

If you don't have your textbook handy where the question comes from, its really worth waiting until you do have it to go over the bits properly rather than being led too much to the answer.

**mqb2766**)2x+90 > 90

so cos(2x+90) is indeed negative.

https://sites.google.com/view/tlmath...e3-trig-graphs

If you don't have your textbook handy where the question comes from, its really worth waiting until you do have it to go over the bits properly rather than being led too much to the answer.

I put the inverse cos of the negative answer I got through a calculator just to check and it turned out positive

Oops don't mind the surded 13 at the end I forgot to scribble it out

https://ibb.co/ThbPNby

Last edited by Rox17; 1 month ago

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#18

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#18

(Original post by

OHH OK I THINK I GOT IT NOW I thought I found the angle but I realised I was finding what cos = 🤦*♀️🤦*♀️🤦*♀️🤦*♀️

I put the inverse cos of the negative answer I got through a calculator just to check and it turned out positive

https://ibb.co/ThbPNby

**Rox17**)OHH OK I THINK I GOT IT NOW I thought I found the angle but I realised I was finding what cos = 🤦*♀️🤦*♀️🤦*♀️🤦*♀️

I put the inverse cos of the negative answer I got through a calculator just to check and it turned out positive

https://ibb.co/ThbPNby

Last edited by mqb2766; 1 month ago

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#19

(Original post by

Looks about right. Note for the cos() being 12/13, it imples sin() is 5/13 as 5: 12:13 is a pythagorean triple

**mqb2766**)Looks about right. Note for the cos() being 12/13, it imples sin() is 5/13 as 5: 12:13 is a pythagorean triple

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