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# 2 c3 trig questions watch

1. if cosX = -8/17 and X is obtuse, find the values of
a) cotX b)cosecX

and

Solve for -180<X<180

secX = 2cosX

2. Setp 1 - find x from

degrees

Now put this value of x into parts a) and b) to get answer.

for second part

so multiply through equation by cos x

then solve this!
Setp 1 - find x from

degrees

Now put this value of x into parts a) and b) to get answer.

for second part

so multiply through equation by cos x

then solve this!
amazing.
how do i solve the second part though

i cant believe i missed out on trig!

4. so

which means that

degrees

question wants all of the solutions between -180 and 180, so using that cos(x) is symmetric about the y axis (meaning ) the other solution is degrees.

We need not consider any further solutions due to the restricted range of answers (-180 to 180) as cos(x) repeats every 360 degrees, so next solution would be outside range.

EDIT

sorry thats rubbish - the solutions are actually

so also consider

Sorry about that, totally forgot it was a squared term!
5. (Original post by SeekerOfKnowledge)
if cosX = -8/17 and X is obtuse, find the values of
a) cotX b)cosecX

and

Solve for -180<X<180

secX = 2cosX

do you have the answers to these questions..I'm struggling to get the answer too

so

which means that

degrees

question wants all of the solutions between -180 and 180, so using that cos(x) is symmetric about the y axis (meaning ) the other solution is degrees.

We need not consider any further solutions due to the restricted range of answers (-180 to 180) as cos(x) repeats every 360 degrees, so next solution would be outside range.

EDIT

sorry thats rubbish - the solutions are actually

so also consider

Sorry about that, totally forgot it was a squared term!
Great Thanks so much!
do you have the answers to these questions..I'm struggling to get the answer too
sure

a) -8/15 b)17/15

for the second part: +- 45 and +-135
8. (Original post by SeekerOfKnowledge)
Great Thanks so much!
how about equations where you cannoy find the identity?

cotX = 5 cosX

so

which means that

degrees

question wants all of the solutions between -180 and 180, so using that cos(x) is symmetric about the y axis (meaning ) the other solution is degrees.

We need not consider any further solutions due to the restricted range of answers (-180 to 180) as cos(x) repeats every 360 degrees, so next solution would be outside range.

EDIT

sorry thats rubbish - the solutions are actually

so also consider

Sorry about that, totally forgot it was a squared term!
how about equations where you cannoy find the identity?

cotX = 5 cosX
10. (Original post by SeekerOfKnowledge)
sure

a) -8/15 b)17/15

for the second part: +- 45 and +-135
thank you...I finally got the answer after 10 minutes of scribbling in my note book.I really need to do some serious C3 revision tomorrow on trig before my exam on wednesday.

good luck btw, when ever you're taking your exam.
11. Do you mean solve cot x = 5 cos x?

If so use that

so

rearrange to get

and then solve!

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