PROVing trigonometry indenties

In summary, the given equation can be simplified to 2sinx + 2cosx / sinxcosx by using the trigonometric identities for tangent, cotangent, cosecant, and secant.
  • #1
ytx123
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0

Homework Statement


(tanx - cosecx)2 - (cotx - secx)2 = 2(cosecx - secx)

Homework Equations


tanx = sinx/cosx
cotx = 1/tanx = cosx/sinx
cosecx = 1/sinx
secx = 1/cosx

The Attempt at a Solution



LHS = (tanx-cosecx)(tanx-cosecx) - (cotx-secx)(cotx-secx)
= tan2x - tanxcosecx - tanxcosecx + cosec2x - cot2x + cotxsecx + cotxsecx
= sin2x/cos2x - (sinx/cosx)(1/sinx) - (sinx/cosx)(1/sinx) + 1/sin2x - cos2x/sin2x + (cosx/sinx)(1/cosx) + (cosx/sinx)(1/cosx) - (1/cos2x)
= sin2x/cos2x - 2sinx/sinxcosx + 1/sin2x - cos2x/sin2x + 2cosx/sinxcosx - 1/cos2x
= sin2x-1 / cos2x + 1 - cos2x / sin2x - 2sinx+2cosx/sinxcosx
= -1 + 1 - 2sinx+2cosx / sinxcosx
= 2sinx + 2cosx / sinxcosx

and I'm stucked
help thanks in advance :)
ps. if i post in the wrong place I am sry cos I am new :/
 
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  • #2
ytx123 said:
LHS = (tanx-cosecx)(tanx-cosecx) - (cotx-secx)(cotx-secx)
= tan2x - tanxcosecx - tanxcosecx + cosec2x - cot2x + cotxsecx + cotxsecx
= sin2x/cos2x - (sinx/cosx)(1/sinx) - (sinx/cosx)(1/sinx) + 1/sin2x - cos2x/sin2x + (cosx/sinx)(1/cosx) + (cosx/sinx)(1/cosx) - (1/cos2x)
= sin2x/cos2x - 2sinx/sinxcosx + 1/sin2x - cos2x/sin2x + 2cosx/sinxcosx - 1/cos2x
= sin2x-1 / cos2x + 1 - cos2x / sin2x - 2sinx+2cosx/sinxcosx
= -1 + 1 - 2sinx+2cosx / sinxcosx
= 2sinx + 2cosx / sinxcosx

You need to use parentheses to clarify addition vs division to avoid making trivial mistakes. You missed a minus sign that's present in the part I bolded. With the correct signs in the last line, you can divide through to obtain the desired result.
 
  • #3
oh! thanks for pointing out my mistake , I've got the answer already :D thanks
 

Related to PROVing trigonometry indenties

1. What is the purpose of proving trigonometry identities?

The purpose of proving trigonometry identities is to show that two trigonometric expressions are equal to each other for all values of the variables involved. This helps to simplify complex expressions and solve equations involving trigonometric functions.

2. How do you prove a trigonometry identity?

To prove a trigonometry identity, you need to use algebraic manipulations and properties of trigonometric functions to transform one side of the equation into the other. This can involve using basic trigonometric identities, such as the Pythagorean identities, and trigonometric identities involving addition, subtraction, double angles, and half angles.

3. Are there any tips for proving trigonometry identities?

One tip for proving trigonometry identities is to start from the more complex side of the equation and work backwards, using algebraic manipulations to simplify the expression. Another tip is to look for patterns and similarities between the two sides of the equation, and use known identities to make connections between them.

4. What are some common mistakes made when proving trigonometry identities?

One common mistake is using incorrect algebraic manipulations, such as canceling out terms that cannot be canceled or making incorrect substitutions. Another mistake is not using the correct identity or property for a given expression. It is important to carefully follow the steps and double check all algebraic manipulations when proving trigonometry identities.

5. How can proving trigonometry identities be useful in real life?

Proving trigonometry identities can be useful in various fields, such as engineering, physics, and astronomy. It allows for simplification of complex equations and can help in solving problems involving angles, distances, and forces. Additionally, understanding trigonometry identities can also help in understanding and using trigonometric functions in practical applications.

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