How do you find the solutions to #8sin^2(3x) = -7sin(3x)#?

Answer 1

Solve 8sin^2 (3x) = - 7sin (3x)

Ans: #-20^@35 and 80^@35#

#8sin^2 (3x) + 7sin (3x) = 0# Put sin (3x) in common factor: #sin (3x)(8sin 3x + 7) = 0#
a. #sin 3x = 0# --> 3x = 0 --> x = 0 #sin 3x = pi# --> #x = pi/3# #sin 3x = 2pi# --> #x = (2pi)/3# b. 8sin (3x) + 7 = 0 --> #sin 3x = -7/8# 3x = - 61.04 --> x = #-20^@35# 3x = 180 - (-61.04) = 241.04 --> #x = 80^@35#
Check by calculator x = 80.35 3x = 241.04 --> sin 3x = -0.875 --> #sin^2 (3x) = 0.77# #8sin^2 (3x) = 0.77(8) = 6.12# --> #-7sin 3x = 7(0.875) = 6.125#. OK
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Answer 2

To find the solutions to the equation 8sin2(3x)=7sin(3x)8 \sin^2(3x) = -7 \sin(3x), first, rewrite it as a quadratic equation in terms of sin(3x)\sin(3x):

8sin2(3x)+7sin(3x)=08 \sin^2(3x) + 7 \sin(3x) = 0

Let y=sin(3x)y = \sin(3x). Then the equation becomes:

8y2+7y=08y^2 + 7y = 0

Now, factor out yy:

y(8y+7)=0y(8y + 7) = 0

This equation has two solutions:

  1. y=0y = 0
  2. 8y+7=08y + 7 = 0

For y=0y = 0, it implies:

sin(3x)=0\sin(3x) = 0

Solving this equation, we get:

3x=nπ, where n is an integer3x = n\pi, \text{ where } n \text{ is an integer}

For 8y+7=08y + 7 = 0, it implies:

8y=78y = -7

Solving for yy, we get:

y=78y = -\frac{7}{8}

Substituting back sin(3x)=78\sin(3x) = -\frac{7}{8}, we get:

3x=arcsin(78)+2nπ or 3x=πarcsin(78)+2nπ3x = \arcsin\left(-\frac{7}{8}\right) + 2n\pi \text{ or } 3x = \pi - \arcsin\left(-\frac{7}{8}\right) + 2n\pi

where nn is an integer.

So, the solutions to the equation 8sin2(3x)=7sin(3x)8 \sin^2(3x) = -7 \sin(3x) are:

x=arcsin(78)3+2nπ3 or x=πarcsin(78)3+2nπ3x = \frac{\arcsin\left(-\frac{7}{8}\right)}{3} + \frac{2n\pi}{3} \text{ or } x = \frac{\pi - \arcsin\left(-\frac{7}{8}\right)}{3} + \frac{2n\pi}{3}

where nn is an integer.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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