Trig functions cross multiplying?

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SUMMARY

The discussion clarifies the misconception surrounding the term "cross multiply" in the context of subtracting fractions involving trigonometric functions. The correct approach involves finding a common denominator rather than cross multiplying. Specifically, when simplifying the expression sin(x)/cos(x) - 2sin(x)cos(x)/1, one should rewrite it as sin(x) - 2sin(x)cos^2(x)/cos(x) after establishing a common denominator. This method ensures accurate simplification of the expression.

PREREQUISITES
  • Understanding of basic trigonometric functions (sine and cosine).
  • Knowledge of fraction operations, specifically addition and subtraction.
  • Familiarity with finding common denominators in rational expressions.
  • Basic algebraic manipulation skills.
NEXT STEPS
  • Study the process of finding common denominators in rational expressions.
  • Learn about simplifying trigonometric expressions using algebraic techniques.
  • Explore the properties of sine and cosine functions in more depth.
  • Practice solving problems involving the subtraction of fractions with trigonometric functions.
USEFUL FOR

Students studying trigonometry, educators teaching algebraic manipulation, and anyone seeking to improve their understanding of fraction operations in mathematical expressions.

musiclover55
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trig functions cross multiplying??

Homework Statement


sinx/cosx - 2sinxcosx/1

Homework Equations


none??

The Attempt at a Solution


when I cross multiply, should it be sinx-2sinxcosx/cosx or sinx-2sinxcos^2x/cosx ??
here's a pic:
http://tinypic.com/r/24fgvmv/6
 
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musiclover55 said:

Homework Statement


sinx/cosx - 2sinxcosx/1

Homework Equations


none??

The Attempt at a Solution


when I cross multiply, should it be sinx-2sinxcosx/cosx or sinx-2sinxcos^2x/cosx ??
here's a pic:
http://tinypic.com/r/24fgvmv/6

You should forget you ever heard the term "cross multiply" since it is interfering with your understanding.

What you have is the difference of two fractions and you need to carry out the subtraction. Both addition and subtraction work the same way: find a common denominator, and once you have the common denominator in both fractions, do the subtraction.

There is no "cross multiply" in either operation.

For example, if I need to simplify 3/5 - 1/4, I would do this:

$$ \frac{3}{5} - \frac{1}{4}$$
$$ =\frac{3}{5}\cdot\frac{4}{4} - \frac{1}{4}\cdot\frac{5}{5}$$
$$ =\frac{12}{20} - \frac{5}{20} = \frac{7}{20}$$
 

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