Math Problem Statement

given that tanx=sinx/cosx solve the following equation forx in the interveal 0°x360°0\degree\le x\le360\degree;2sin^2x-cosx=1

Solution

We are given the equation:

2sin2xcosx=12\sin^2x - \cos x = 1

We need to solve this equation for xx in the interval 0x3600^\circ \leq x \leq 360^\circ.

Step 1: Substituting for sin2x\sin^2 x

We can use the Pythagorean identity: sin2x=1cos2x\sin^2 x = 1 - \cos^2 x Substitute sin2x\sin^2 x into the equation:

2(1cos2x)cosx=12(1 - \cos^2 x) - \cos x = 1

Step 2: Simplifying the equation

Expand and simplify:

2(1)2cos2xcosx=12(1) - 2\cos^2 x - \cos x = 1

22cos2xcosx=12 - 2\cos^2 x - \cos x = 1

Now, subtract 1 from both sides:

12cos2xcosx=01 - 2\cos^2 x - \cos x = 0

Step 3: Rearranging the equation

Rearrange it as a quadratic equation in terms of cosx\cos x:

2cos2x+cosx1=02\cos^2 x + \cos x - 1 = 0

Step 4: Solving the quadratic equation

We can solve this quadratic equation using the quadratic formula. The quadratic formula is given by:

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

For the equation 2cos2x+cosx1=02\cos^2 x + \cos x - 1 = 0, the coefficients are a=2a = 2, b=1b = 1, and c=1c = -1. Substituting into the quadratic formula:

cosx=1±124(2)(1)2(2)\cos x = \frac{-1 \pm \sqrt{1^2 - 4(2)(-1)}}{2(2)} cosx=1±1+84\cos x = \frac{-1 \pm \sqrt{1 + 8}}{4} cosx=1±94\cos x = \frac{-1 \pm \sqrt{9}}{4} cosx=1±34\cos x = \frac{-1 \pm 3}{4}

This gives us two solutions for cosx\cos x:

  1. cosx=1+34=24=12\cos x = \frac{-1 + 3}{4} = \frac{2}{4} = \frac{1}{2}
  2. cosx=134=44=1\cos x = \frac{-1 - 3}{4} = \frac{-4}{4} = -1

Step 5: Finding the angles

Case 1: cosx=12\cos x = \frac{1}{2}

The angles where cosx=12\cos x = \frac{1}{2} in the interval 0x3600^\circ \leq x \leq 360^\circ are: x=60,300x = 60^\circ, 300^\circ

Case 2: cosx=1\cos x = -1

The angle where cosx=1\cos x = -1 in the interval 0x3600^\circ \leq x \leq 360^\circ is: x=180x = 180^\circ

Step 6: Final solution

The solutions for xx are: x=60,180,300x = 60^\circ, 180^\circ, 300^\circ

Would you like more details or have any questions?

Here are 5 related questions for practice:

  1. Solve 2cos2xsinx=02\cos^2 x - \sin x = 0 in the interval 0x3600^\circ \leq x \leq 360^\circ.
  2. Solve sin2x=cosx\sin 2x = \cos x in the same interval.
  3. Find the general solution for sin2x2sinx=0\sin^2 x - 2\sin x = 0.
  4. Solve 3cos2x4cosx+1=03\cos^2 x - 4\cos x + 1 = 0 in 0x3600^\circ \leq x \leq 360^\circ.
  5. Solve cos2x+sinx=1\cos^2 x + \sin x = 1 in the given interval.

Tip: When solving trigonometric equations, remember to consider all possible angles within the given interval that satisfy the equation!

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Quadratic Equations
Pythagorean Identity

Formulas

sin²x = 1 - cos²x
Quadratic formula: x = (-b ± √(b² - 4ac)) / 2a

Theorems

Pythagorean Identity
Quadratic Formula

Suitable Grade Level

Grades 10-12