use the law of cosines to find the value of 2⋅3⋅4 cosθ

- anonymous

use the law of cosines to find the value of 2⋅3⋅4 cosθ

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- anonymous

@dan815

- anonymous

@taramgrant0543664

- anonymous

what do you mean by
2⋅3⋅4 cosθ
You mean \[\cos 2\theta\quad,\cos3\theta,\quad \cos3\theta\]?

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## More answers

- taramgrant0543664

Do you have a triangle that corresponds to this question?

- anonymous

|dw:1438361201942:dw|

- taramgrant0543664

This is the law c^2=A^2+b^2−2abcosC

- anonymous

21

- taramgrant0543664

4=16+9-2(4)(3)cosC
21=24cosC
0.875=cosC
C= 28.96

- anonymous

A. 24
B. 21
C. -24
D. -21

- taramgrant0543664

I just understood the whole 2,3,4 thing and ya it is equal to 21 I just assume you had to solve for the angle

- anonymous

so is it 21 then

- taramgrant0543664

Yes it is

- anonymous

thanks

- anonymous

can you help me with another question please? @taramgrant0543664

- taramgrant0543664

I can try!

- anonymous

ok

- anonymous

|dw:1438362470160:dw|

- anonymous

true or false

- anonymous

@taramgrant0543664

- anonymous

nvm

- anonymous

wrong problem

- anonymous

Suppose a triangle has sides a, b, and c, and that a2 + b2 > c2. Let be the measure of the angle opposite the side of length c. Which of the following must be true? Check all that apply.

- anonymous

A. cos < 0
B. cos > 0
C. is an acute angle.
D. The triangle in question is a right triangle.

- anonymous

@taramgrant0543664

- taramgrant0543664

I'd like to think it would be D but I'm not certain

- anonymous

its more than 1 answer

- anonymous

i think its a and d

- anonymous

what do you think

- taramgrant0543664

A and D that's what I'm thinking

- anonymous

yup yup

- anonymous

Suppose a triangle has sides a, b, and c, and the angle opposite the side of length b is obtuse. What must be true?

- anonymous

how about this one

- anonymous

A. b2 + c2 < a2
B. a2 + c2 > b2
C. a2 + c2 < b2
D. a2 + b2 < c2

- anonymous

@taramgrant0543664

- anonymous

i think it a @taramgrant0543664

- taramgrant0543664

Ya I was trying to think it out and I was thinking it was A but I was testing out the other options too to double check

- anonymous

that good

- anonymous

it wasnt a

- anonymous

its aight

- phi

Suppose a triangle has sides a, b, and c, and the angle opposite the side of length b is obtuse. What must be true?
they tell you about angle B (opposite side b) is bigger than 90 degrees (i.e. obtuse)
I would write down the law of cosines in the form that uses angle B (because that is the angle we know about)
b^2 = a^2 + c^2 - 2 a c cos B
next, we (should!) know cos of an angle bigger than 90 (but less than 180) is negative
in other words - 2 ac cos B will turn into a positive number (because -2 * neg cos will be positive)
in other words, we can say
b^2 = a^2 + c^2 + more
if we subtract off more from the right side, the right side will no longer be equal to the left side ... it will be too small.
we can say
b^2 > a^2 + c^2
or (means the same thing)
a^2 + c^2 < b^2

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