Lesson 19 Dealing with Trigonometric Functions

19.1 The Sin function

The Sin function returns the sine value of an angle. We need to convert the angle to radian as Visual Basic 2019 cannot deal with an angle in degree. The conversion is based on the following equation:

π radian= 180º

so 1º=π/180 radian

The issue is how to get the exact value of π? We can use π=3.14159 but it will not be accurate. To get the exact value of π, we use the arcsine function, i.e. is Asin.

Using the equation

 sin(π/2)=1, 
 Asin(1)=π/2

therefore,

π=2Asin(1)

The syntax of  the Sin function in Visual Basic 2019 is

Math.Sin(Angle in radian)

Example 19.1

In this example, we use pi to represent π and assign the value of π using the formula pi = 2*Math.Asin(1). We use the function Round to round the value of sine to four decimal places.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim pi As Single
pi = 2*Math.Asin(1)
MsgBox("Sin 90 is" & Math.Round(Math.Sin(pi / 2), 4))
End Sub

The Output Interface

19.2 The Cos function

In Visual Basic 2019, the Cos function returns the Cosine value of an angle. The syntax is

Math.Cos(Angle in radian)

Example 19.2

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim pi As Single
pi = 2*Math.Asin(1)
MsgBox("Cos 180 is " & Math.Round(Math.Cos(pi), 4))
End Sub

 The Output

 

19.3 The Tan function

In Visual Basic 2019, the Tan function returns the tangent value of an angle. The syntax is

Math.Tan(Angle in radian)

Example 19.3

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim pi As Single
pi = 2 * Math.Asin(1)
MsgBox("Tan 45 is " & Math.Round(Math.Tan(pi / 4)), 4)
End Sub

The Output

19.4 The Asin Function

The Asin function returns the value of arcsine (inverse sine ) and it represents the angle that corresponds to the sine value. For example, sin90º = 1,  so asin(1)=90º

In Visual Basic 2019, the value of arcsine is expressed in terms of radian. To convert the value to degree, we use the formula 1 radian=180º/π, where π=2Asin(1).

Example 19.4

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button7.Click
Dim pi As Single
pi = 2 * Math.Asin(1)
MsgBox("Asin(1)is " & Math.Round(Math.Asin(1) * 180 / pi), 4)
End Sub

The Output

19.5 The Acos Function

In Visual Basic 2019, the Acos function returns the value of arc cosine (inverse cosine ) and it represents the angle that corresponds to the cos value. For example, cos90º = 0,  so acos(0)=90º

 

Example 19.5

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button7.Click
Dim pi As Single
pi = 2 * Math.Asin(1)
MsgBox("Asin(1)is " & Math.Round(Math.Acos(1) * 180 / pi), 4)
End Sub

19.6 The Atan Function

In Visual Basic 2019, the Atan function returns the value of arc tangent (inverse tangent) and it represents the angle that corresponds to the tan value. For example, tan45º = 1,  so atan(1)=45º

Example 19.6

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button7.Click
Dim pi As Single
pi = 2 * Math.Asin(1)
MsgBox("Asin(1)is " & Math.Round(Math.Atan(1) * 180 / pi), 4)
End Sub

The Output

 19.7 Applications

Trigonometric functions can be used to solve various mathematical problems. Common examples are problems involving the sine rule, the cosine rule, trigonometric identities, trigonometric equations, the projectile equation and more.

Example 19.7 The Sine Rule

For example, in a triangle ABC, give angle  A=60 and angle B=30 respectively, length BC denoted by a=4  you can calculate length AC (denoted by b).

The formula is

a/sinA=b/sinB, so b=asinB/sinA

Private Sub Button8_Click(sender As Object, e As EventArgs) Handles Button8.Click
Dim pi As Single
Dim A As Single, B As Single, x As Single
pi = 2 * Math.Asin(1)
A = 60 * pi / 180
B = 40 * pi / 180
x = 4
MsgBox("AC= " & Math.Round((x * Math.Sin(A) / Math.Sin(B)), 4))
End Sub

The Output