Math Problem Statement

Can I use 30,45,90 trig values to solve all these

Can I use 30, 45, 90 trig values to solve all these?

Solution

Yes, you can use the known exact trigonometric values for 3030^\circ, 4545^\circ, and 9090^\circ (as well as their complements and periodic properties) to solve all of these problems. Here's how:

  1. Problem 1: cos(330)\cos(330^\circ)
    Use the fact that 330=36030330^\circ = 360^\circ - 30^\circ. This places the angle in the 4th quadrant where cosine is positive, and we know:
    cos(330)=cos(30)=32.\cos(330^\circ) = \cos(30^\circ) = \frac{\sqrt{3}}{2}.

  2. Problem 2: sec(315)\sec(-315^\circ)
    First, simplify the angle using the periodic property 360360^\circ:
    315+360=45.-315^\circ + 360^\circ = 45^\circ.
    Since sec(θ)=1cos(θ)\sec(\theta) = \frac{1}{\cos(\theta)}, we calculate:
    sec(315)=sec(45)=1cos(45)=122=2.\sec(-315^\circ) = \sec(45^\circ) = \frac{1}{\cos(45^\circ)} = \frac{1}{\frac{\sqrt{2}}{2}} = \sqrt{2}.

  3. Problem 3: sin(450)\sin(450^\circ)
    Simplify 450450^\circ using periodicity:
    450360=90.450^\circ - 360^\circ = 90^\circ.
    Therefore, sin(450)=sin(90)=1.\sin(450^\circ) = \sin(90^\circ) = 1.

  4. Problem 4: cot(120)\cot(120^\circ)
    Rewrite 120120^\circ as 18060180^\circ - 60^\circ. This places the angle in the 2nd quadrant where tangent (and cotangent) is negative.
    Using cot(θ)=cos(θ)sin(θ)\cot(\theta) = \frac{\cos(\theta)}{\sin(\theta)}, we know:
    cot(120)=cot(60)=cos(60)sin(60)=1232=13=33.\cot(120^\circ) = -\cot(60^\circ) = -\frac{\cos(60^\circ)}{\sin(60^\circ)} = -\frac{\frac{1}{2}}{\frac{\sqrt{3}}{2}} = -\frac{1}{\sqrt{3}} = -\frac{\sqrt{3}}{3}.


Final Results:

  1. cos(330)=32\cos(330^\circ) = \frac{\sqrt{3}}{2}
  2. sec(315)=2\sec(-315^\circ) = \sqrt{2}
  3. sin(450)=1\sin(450^\circ) = 1
  4. cot(120)=33\cot(120^\circ) = -\frac{\sqrt{3}}{3}

Would you like further explanations or visual aids for any of these?


Here are 5 related questions for further learning:

  1. How do trigonometric functions behave in each quadrant?
  2. What is the relationship between secant and cosine?
  3. How can you quickly determine cotangent using reference angles?
  4. Why are trigonometric functions periodic, and what are their periods?
  5. How do complementary and supplementary angles relate to trigonometric functions?

Tip: Always simplify angles using periodicity (360360^\circ or 2π2\pi) to make calculations easier!

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Math Problem Analysis

Mathematical Concepts

Trigonometric functions
Reference angles
Quadrants and periodicity in trigonometry

Formulas

cos(θ)
sec(θ) = 1/cos(θ)
sin(θ)
cot(θ) = cos(θ)/sin(θ)

Theorems

Periodic properties of trigonometric functions
Reference angle theorem
Trigonometric values for 30°, 45°, and 90°

Suitable Grade Level

Grades 10-12