Solving Trigonometric Equations

E.g.1


sinegraph

 

Solve sin x = 0.5 for 0 ≤ x ≤ 360
sin x = 0.5
x = 300
Since y = 0.5 line crosses the sine curve at two points, there are two solutions.
Now, look at the symmetry of the graph; the two values of x are 300 and 1500.
x = 30 and 150.

E.g.2

sinegraph

 

Solve cos x = -0.5 for 0 ≤ x ≤ 360
cos x = -0.5
x = 1200
Since y = -0.5 line crosses the sine curve at two points, there are two solutions.
Now, look at the symmetry of the graph; the two values of x are 1200 and 2400.
x = 120 and 240.

E.g.3

Solve sin (x +10) = 0.5 for 0 ≤ x ≤ 360
From example 1,
(x + 10) = 300
There are two values for (x +10) that satisfy the equation; they are 300 and 1500
x + 10 = 30 or x + 10 = 150
x = 20 or x = 140

E.g.4

Solve 1 + 2 sin x = 2 for 0 ≤ x ≤ 360
2 sin x = 1
sin x = 0.5
From example 1,
x = 300
There are two values for x that satisfy the equation; they are 300 and 1500
x = 30 or x = 150.


Now, in order to complement what you have just learnt, work out the following questions:


  1. Solve 2 sin x = 1.5 for 0 ≤ x ≤ 360
  2. Solve 1 + 3 cos x = 2 for 0 ≤ x ≤ 360
  3. Solve sin (2x - 10) = 0.7 for 0 ≤ x ≤ 360
  4. Solve tan (x -30) = 0.7 for 0 ≤ x ≤ 360
  5. Solve cos (2x -20) = 0.5 for 0 ≤ x ≤ 360
  6. Solve sin2 x = 0.25 for 0 ≤ x ≤ 360
  7. Solve sin 2x = 0.5 for 0 ≤ x ≤ 360
  8. Solve 1 + 3 sin 2x = 2 for 0 ≤ x ≤ 360


 

 

Recommended Reading

 

Maths is challenging; so is finding the right book. K A Stroud, in this book, cleverly managed to make all the major topics crystal clear with plenty of examples; popularity of the book speak for itself - 7th edition in print.

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