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# 2 questions, i am very confused on

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1. Angle  α lies in quadrant II , and tanα=−12/5 . Angle  β lies in quadrant IV , and cosβ=3/5 .

What is the exact value of cos(α+β) ?

cos(α+β) =

Second question deleted by Melody.

One question per post and see if you can learn from the first answer before you post the second question.

Mar 11, 2020
edited by Melody  Mar 11, 2020

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1. Angle  α lies in quadrant II , and tanα=−12/5 . Angle  β lies in quadrant IV , and cosβ=3/5 .

What is the exact value of cos(α+β) ?

Remember that

sin(angle) is the y value over the hypotenuse.

cos(angle) is the x value over the hypotenuse.

$$tan(angle)=\frac{sin(angle)}{cos(angle)}=\frac{y}{x}$$

Here is a pic that should help: and

$$cos(\alpha+\beta)=cos\alpha cos\beta - sin\alpha sin\beta \\$$

Now see if you can work it out yourself.   :)

Mar 11, 2020
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would it be 33/65 ?

jjennylove  Mar 11, 2020
#3
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beats me. How about including some working so I can see if your fractions are correct?

Melody  Mar 11, 2020
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Good work.

Melody  Mar 11, 2020
edited by Melody  Mar 11, 2020
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thank you! jjennylove  Mar 11, 2020
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You are very welcome.

There is a lot that can be learned from the way I have drawn the pic. See if you can get as much as possible out of it. Melody  Mar 11, 2020