SOLUTION: Find all solutions to the equation. (4 points) sin2x + sin x = 0 This is what I have so far. Can you please double check my work? sin2x + sin x = 0 sin x ( sin x + 1) =

Algebra ->  Trigonometry-basics -> SOLUTION: Find all solutions to the equation. (4 points) sin2x + sin x = 0 This is what I have so far. Can you please double check my work? sin2x + sin x = 0 sin x ( sin x + 1) =       Log On


   



Question 979386: Find all solutions to the equation. (4 points)
sin2x + sin x = 0

This is what I have so far. Can you please double check my work?
sin2x + sin x = 0
sin x ( sin x + 1) = 0

sin x = 0 sin x = -1
x= n*pi x= (2n+1) pi

Found 2 solutions by jim_thompson5910, Edwin McCravy:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
I'm assuming you have sin%5E2%28x%29+%2B+sin%28x%29+=+0

If sin%28x%29+=+0, then it is true that x+=+n%2Api where n is any integer. Ie, x is a multiple of pi.

If sin%28x%29+=+-1, then x+=+%283pi%29%2F2+%2B+2pi%2An where n is any integer.

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Put the two together to get this solution set

x+=+n%2Api or x+=+%283pi%29%2F2+%2B+2pi%2An where n is any integer.

Answer by Edwin McCravy(20063) About Me  (Show Source):
You can put this solution on YOUR website!
I think you're confusing sin(2x) with sin2(x)

You cannot treat trig functions like "sin" and "cos" as 
if they behaved like multication, because they don't!
To simplify trigonometric expressions and equations,
we us IDENTITIES:

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If the problem were as you solved it, you would
have had it half correct:

sin%5E2%28x%29+%2B+sin%28x%29%22%22=%22%22%220%22

You would do as you did and factor out sin(x):

sin%28x%29%28sin%28x%29%5E%22%22%2B1%29%22%22=%22%22%220%22

sin%28x%29=0,     sin%28x%29%2B1=0

x=n%2Api,      sin%28x%29=-1
                    x=3pi%2F2%2B2pi%2An
                    x=3pi%2F2%2B4pi%2An%2F2
                    x=%283%2B4n%29%28pi%2F2%29

Your solution of the second part here was incorrect.

HOWEVER, THIS IS NOT THE EQUATION YOU ARE TO SOLVE!!!

Here is the problem:

sin%282x%29+%2B+sin%28x%29%22%22=%22%22%220%22

You cannot factor.

What you do is use the identity sin%282theta%29=2sin%28theta%29cos%28theta%29

2sin%28x%29cos%28x%29%2Bsin%28x%29%22%22=%22%22%220%22

Now you can factor out sin(x)

sin%28x%29%282cos%28x%29%2B1%29=0

sin%28x%29,      2cos%28x%29%2B1=0
                   2cos%28x%29=-1
x=n%2Api,      cos%28x%29=-1%2F2
                    x=2pi%2F3%2B2pi%2An   and   x=4pi%2F3%2B2pi%2An
                    x=2pi%2F3%2B6pi%2An%2F3       x=4pi%2F3%2B6pi%2An%2F3
                    x=%282%2B6n%29%28pi%2F3%29        x=%284%2B6n%29%28pi%2F3%29
                    x=2%281%2B3n%29%28pi%2F3%29       x=2%282%2B3n%29%28pi%2F3%29
                    x=%281%2B3n%29%282pi%2F3%29       x=%282%2B3n%29%282pi%2F3%29

Edwin