Math Problem Statement

12cos^2 x - sinx = 11

Solution

To solve the equation 12cos2xsinx=1112 \cos^2 x - \sin x = 11, let's go step by step.

Step 1: Use the Pythagorean identity

We know that cos2x+sin2x=1\cos^2 x + \sin^2 x = 1. So, we can express cos2x\cos^2 x in terms of sinx\sin x.

cos2x=1sin2x\cos^2 x = 1 - \sin^2 x

Step 2: Substitute into the equation

Now, substitute cos2x=1sin2x\cos^2 x = 1 - \sin^2 x into the original equation:

12(1sin2x)sinx=1112 (1 - \sin^2 x) - \sin x = 11

Step 3: Simplify the equation

Distribute the 12 on the left side:

1212sin2xsinx=1112 - 12 \sin^2 x - \sin x = 11

Now, subtract 11 from both sides:

1212sin2xsinx11=012 - 12 \sin^2 x - \sin x - 11 = 0

This simplifies to:

112sin2xsinx=01 - 12 \sin^2 x - \sin x = 0

Step 4: Rearrange the equation

Now, we have a quadratic equation in terms of sinx\sin x:

12sin2xsinx+1=0-12 \sin^2 x - \sin x + 1 = 0

Multiply through by -1 to simplify:

12sin2x+sinx1=012 \sin^2 x + \sin x - 1 = 0

Step 5: Solve the quadratic equation

Now we have a quadratic equation in sinx\sin x:

12sin2x+sinx1=012 \sin^2 x + \sin x - 1 = 0

We can solve this using the quadratic formula:

sinx=b±b24ac2a\sin x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

where a=12a = 12, b=1b = 1, and c=1c = -1. Substituting these values into the formula:

sinx=1±124(12)(1)2(12)\sin x = \frac{-1 \pm \sqrt{1^2 - 4(12)(-1)}}{2(12)}

sinx=1±1+4824\sin x = \frac{-1 \pm \sqrt{1 + 48}}{24}

sinx=1±4924\sin x = \frac{-1 \pm \sqrt{49}}{24}

sinx=1±724\sin x = \frac{-1 \pm 7}{24}

Step 6: Solve for the two possible values of sinx\sin x

  1. sinx=1+724=624=14\sin x = \frac{-1 + 7}{24} = \frac{6}{24} = \frac{1}{4}
  2. sinx=1724=824=13\sin x = \frac{-1 - 7}{24} = \frac{-8}{24} = -\frac{1}{3}

Step 7: Find the corresponding xx values

We now have two possible values for sinx\sin x:

  1. sinx=14\sin x = \frac{1}{4}
  2. sinx=13\sin x = -\frac{1}{3}

We can solve for xx in each case using inverse sine.

  1. x=sin1(14)x = \sin^{-1} \left(\frac{1}{4}\right)
  2. x=sin1(13)x = \sin^{-1} \left(-\frac{1}{3}\right)

Let me know if you'd like me to calculate these specific values or if you'd like more details on any of the steps!


Here are 5 related questions to expand on this:

  1. How do you solve quadratic equations with trigonometric functions?
  2. How do you apply the Pythagorean identity to simplify trigonometric equations?
  3. What are the general solutions for trigonometric equations like sinx=14\sin x = \frac{1}{4} or sinx=13\sin x = -\frac{1}{3}?
  4. How does the inverse sine function help in finding the angle corresponding to a sine value?
  5. What are the possible solutions for trigonometric equations on different intervals, such as [0,2π][0, 2\pi]?

Tip: When solving trigonometric equations, always remember to consider multiple possible solutions within the required interval.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Quadratic Equations
Pythagorean Identity

Formulas

Pythagorean identity: cos^2 x + sin^2 x = 1
Quadratic formula: x = (-b ± √(b² - 4ac)) / 2a

Theorems

Pythagorean identity
Quadratic formula

Suitable Grade Level

Grades 10-12