MHB Adding Trigonometric Functions

AI Thread Summary
The discussion revolves around the challenge of adding two trigonometric functions: 20-10cos(x*pi/4) and 30+20sin(x*pi/4). The user struggles to find a suitable formula for combining these functions and expresses confusion over the addition/subtraction of trigonometric functions. A helpful formula is provided, which states that a*sin(θ) - b*cos(θ) can be expressed as √(a²+b²)sin(θ - φ), with φ defined by the ratio of b to a. The user acknowledges the clarity gained after understanding this formula. This exchange highlights the importance of specific trigonometric identities in solving complex problems.
TrigEatsMe
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I've muddled my way through the majority of my weekend assignment and I'm stuck on a problem where I need to add two formulas together.

1.) 20-10cos(x*pi/4)
2.) 30+20sin(x*pi/4)

I end up with a sinusoidal function which I can then graph and determine the max, min, etc.

We recently went over the addition/subtraction of trigonometric functions using formulas, but none of them match up with this kind of question. I'm missing something.
 
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TrigEatsMe said:
I've muddled my way through the majority of my weekend assignment and I'm stuck on a problem where I need to add two formulas together.

1.) 20-10cos(x*pi/4)
2.) 30+20sin(x*pi/4)

I end up with a sinusoidal function which I can then graph and determine the max, min, etc.

We recently went over the addition/subtraction of trigonometric functions using formulas, but none of them match up with this kind of question. I'm missing something.
The formula you need here is the one that says $a\sin\theta - b\cos\theta = \sqrt{a^2+b^2}\sin(\theta - \phi)$, where $\tan\phi = \dfrac ba.$
 
Got it -- weird how it clicks the following day sometimes. THanks! :)
 
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