# C3 trig helpWatch

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#1
This is to do with trig identities. It's probably really simple but I'm having a mind block ><

Thankyou!

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5 years ago
#2
replace tan with a well known combination of sin and cos...
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5 years ago
#3
Whenever I teach identities I encourage all students to have a sheet which:
(1) Lists all identities and subtle manipulations
(2) Methods in which to prove identities

You have some good advice in the post above.
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#4
(Original post by the bear)
replace tan with a well known combination of sin and cos...
I originally tried that and got an answer which is wrong.

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5 years ago
#5
(Original post by kendellex)
I originally tried that and got an answer which is wrong.

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You didn't though

cosx/cosx = 1
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5 years ago
#6
(Original post by kendellex)
I originally tried that and got an answer which is wrong.
What did you do after the fraction line?
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5 years ago
#7
(Original post by kendellex)
I originally tried that and got an answer which is wrong.

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Would the last line not end up as (1+sin(2theta))/cos(2theta) ?
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#8
I just multiplied it by cosx - sinx to change it out of a fraction

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5 years ago
#9
(Original post by kendellex)
I just multiplied it by cosx - sinx to change it out of a fraction

So where did your denominator go?
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5 years ago
#10
(Original post by kendellex)
I just multiplied it by cosx - sinx to change it out of a fraction

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But you haven't done that.

If I multiply the fraction 1/2 by 5 I dont get 5/10 I get 5/2.
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5 years ago
#11
I ended up with 1+sin theta/ 1- sin theta
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5 years ago
#12
(Original post by kendellex)
I originally tried that and got an answer which is wrong.

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Have you been given the answer to the question?
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5 years ago
#13
1+sin theta/ 1-sin theta
then multipliying the reciprocal to the numerator
so it goes 1+sin theta (x) 1/1-sin theta
then it ended up as (1-sin theta+sin theta-sin(squared)theta)
the -sin and +sin cancels out so I was left with (1-Sin(squared)Theta) Which is cos(squared)Theta.

Is this correct? I'm doing C3 too so I need help haha
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5 years ago
#14
(Original post by brent_)
1+sin theta/ 1-sin theta
then multipliying the reciprocal to the numerator
so it goes 1+sin theta (x) 1/1-sin theta
then it ended up as (1-sin theta+sin theta-sin(squared)theta)
the -sin and +sin cancels out so I was left with (1-Sin(squared)Theta) Which is cos(squared)Theta.

Is this correct? I'm doing C3 too so I need help haha
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5 years ago
#15
(Original post by TenOfThem)
I evaluated 1+sin/cos
1-sin/cos
And unfortunately ended up with that.
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5 years ago
#16
(Original post by brent_)
I evaluated 1+sin/cos
1-sin/cos
And unfortunately ended up with that.
You think that

Where did the s go
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5 years ago
#17
(Original post by kendellex)
This is to do with trig identities. It's probably really simple but I'm having a mind block ><

Thankyou!

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Is it not just tan(theta + 45)

expand it out using the double angle formulas remembering that tan(45) = 1
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5 years ago
#18
(Original post by Student10011)
Is it not just tan(theta + 45)

expand it out using the double angle formulas remembering that tan(45) = 1
Yes, it is
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#19
(Original post by Student10011)
Is it not just tan(theta + 45)

expand it out using the double angle formulas remembering that tan(45) = 1
Thank you! I honestly forgot that rule >< I've got it now (:

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5 years ago
#20
(Original post by kendellex)
Thank you! I honestly forgot that rule >< I've got it now (:

You may have solved this but - have you reflected on your error from earlier - do you know what you did wrong
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