Valhalla Legends Forums Archive | Yoni's Math Forum | Some Trig Problems

AuthorMessageTime
hismajesty
Show work:

Verify each identity
[img]http://img226.imageshack.us/img226/2060/10wi.png[/img]

Solve each equation over the interval [0,2pi]. Give exact answers (I guess that means radian form.)
[img]http://img226.imageshack.us/img226/5821/28xp1.png[/img]

Find the complete solution set for each equation. Give exact answers.
[img]http://img226.imageshack.us/img226/8933/32zj.png[/img]

Approximate the solutions of the equation in the interval [0,2pi]. Use a graphing calculator.
[img]http://img214.imageshack.us/img214/4021/41sd.png[/img]
April 30, 2006, 6:43 PM
Rule
By answering these questions, would I be doing your homework for you?
May 1, 2006, 1:55 AM
hismajesty
[quote author=Rule link=topic=14907.msg151648#msg151648 date=1146448548]
By answering these questions, would I be doing your homework for you?

[/quote]

Yes, technically. However, this doesn't go down in the gradebook as homework...I just need it for our quiz (it's like a review) which is on Tuesday. Our quizzes are open notes, and I'll need the examples in order to figure out the quiz.
May 1, 2006, 10:19 AM
Yoni
[u]One[/u]

A few loose hints, that probably work most of the time:

Hint 1. Use basic, well-known and accepted trigonometry identities (such as sin(90-x) = cos(x), and tan(x) = 1/cot(x)).
Hint 2. Use the laws of algebra.
Hint 3. Don't work with sec and csc. Change sec to 1/cos and csc to 1/sin.

Note: I just made these up, some or all of them might be unusable on some questions.

Example:

sec(x) - cos(x) =
[sec is not an acceptable form - hint #3]
= (1/cos(x)) - cos(x) =
[laws of algebra: fractions - hint #2]
= (1 - cos^2(x)) / cos(x) =
[known trigonometric identities: sin^2(x) + cos^2(x) = 1 - hint #1]
= sin^2(x) / cos(x) =
[known trigonometric identities: sin(x) / cos(x) = tan(x) - hint #1]
= sin(x) tan(x)

[hr]

[u]Two[/u]

As for solving equations exactly, try to convert it to algebra.
All squares of sines and cosines can be interchanged using a well known identity, so if you can reach an equation containing only sines (and squares of sines) or only cosines (and squares of cosines), you can algebraically solve it as a quadratic equation, and then trigonometrically solve 1 or 2 equations of the form sin(x) = p or cos(x) = p.

[hr]

[u]Three[/u]

Same as "Two", but find all answers, not just in a specific interval. It depends on you knowing the general solution to the basic equation sin(x) = p or cos(x) = p. You can convert tangents to sin/cos's and reach quadratic equations in the same way mentioned above.

[hr]

[u]Four[/u]

Ok, using a graphical calculator is rather technical. Post if you still need help with this one ;)
May 1, 2006, 6:13 PM

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