Drawing Trigonometric Graphs The Basic Graphs You should

Drawing Trigonometric Graphs.

The Basic Graphs. You should already be familiar with the following graphs: Y = SIN X

Y= COS X

Y = TAN X

Changing Trigonometric Graphs. You should know how the following graphs differ from the basic trigonometric graphs: Y= 2 SIN X The 2 in front of the sin x changes the “amplitude” of the graph.

Y = 5 COS X As expected the amplitude of the graph is now 5. Hence the graph has a maximum value of 5 and a minimum value of – 5.

Y = SIN 2 X By introducing the 2 in front of the X , the “period” of the graph now becomes 360 o 2 = 180 o.

Y= COS 6 X The period of the graph has now become 360 o 6 = 60 o as expected.

Y= SIN X + 1 The plus 1 has the effect of “translating” the graph one square parallel to the y axis.

Y = COS X - 5 The cosine graph is translated 5 squares downwards parallel to the y axis.

Y= – SIN X The minus sign in front of the function “reflects” the whole graph in the X axis.

Y = – COS X As expected the cosine graph is reflected in the X axis.

Summary Of Effects. (1) Y= K COS X & Y = K SINX +k -k The amplitude of the function is “K”. (2) Y = COS KX & Y = SIN KX 360 K The period of the function is “ 360 k”.

(3) Y= COS X + K & Y = SIN X + K +k -k Translates the graph + K or – K parallel to the y axis. (4) Y = - COS X & Y = - SIN X. Y = - COS X Reflects the graph in the x axis.

Combining The Effects. We are now going to draw more complex trigonometric graphs like the one shown above, by considering what each part of the equation does to the graph of the equation.

Example 1. Draw the graph of : y = 4 sin x 4 y = 4 sin 2 x + 3 Solution. Draw the graph of : y = sin x y = 4 sin 2 x 180 o y = 4 sin 2 x + 3 +3

Example 2 y = - 6 cos 5 x Draw the graph y = 2 – 6 cos 5 x Solution. Draw the graph of : y = cos x y = 2 – 6 cos 5 x y= 6 cos 5 x 72 o 6

Creating A Phase Shift. Shown below is the graph of y = sin xo Now compare it with the graph of y= sin( x - 60 o) + 60 o The graph is translated 60 o to the right parallel to the x axis.

Shown below is the graph of y = cos x. Now compare it to the graph of y = cos ( x + 45 o) -45 o The graph is translated 45 o to the left parallel to the x axis.

From the previous examples we can now see that the equation: y = cos ( x - k ) & y = sin ( x - k) translates the graph ko to the right parallel to the x axis. + ko y = cos (x-k) y = cos x From the previous examples we can now see that the equation: y = cos ( x + k ) & y = sin ( x + k) translates the graph ko to the left parallel to the x axis.