Trigonometry, different products of sine and cosine

In summary, the conversation discusses the different values among the trigonometric expressions sin a sin b, sin a cos b, cos a sin b, and cos a cos b in a right angled triangle with angles a, b, and 90deg. The solution lies in using the trigonometric identity sin(x) = cos(90 - x) and knowing that a and b are not equal. The values for all the expressions are different when a < b, as sina = cosb and sinb = cosa. Drawing out a right-angled triangle and substituting values can help understand this concept.
  • #1
Trail_Builder
149
0

Homework Statement



There is a right angled triangle, with the following angles, a, b, and 90deg.

If a < b, how many different values are there among the following expressions?

sin a sin b, sin a cos b, cos a sin b, cos a cos b

Homework Equations





The Attempt at a Solution



I don't really know any trigonometric identies and I am guessing that's where the solution lies :S
 
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  • #2
Here is a trigonometric identity: sin(x) = cos(90 - x)
Try to use it.
 
  • #3
:S

sorry i still don't know how i would use it
 
  • #4
What is the sum of the 3 angles in a triangle?
And if you know that one of them is a right angle, then what is the sum of the other 2?
 
  • #5
Trail_Builder said:

Homework Statement



There is a right angled triangle, with the following angles, a, b, and 90deg.

If a < b, how many different values are there among the following expressions?

sin a sin b, sin a cos b, cos a sin b, cos a cos b

Homework Equations





The Attempt at a Solution



I don't really know any trigonometric identies and I am guessing that's where the solution lies :S

antonantal said:
Here is a trigonometric identity: sin(x) = cos(90 - x)
Try to use it.

Trail_Builder said:
:S

sorry i still don't know how i would use it
The point is that sin(a)= cos(b) and sin(b)= cos(a).
 
  • #6
there are 3 different values there. the oiint in telling you that b>a is to make sure you know that b does not equal to a. because, is b=a, the values for all the expressions will be the same. but in this case, since the 2 angles are different, sina=cosb. also, sinb=cosa. if you don't get this, try drawing out a right-angled triangle and label it's angles. use 3,4,5 as the length of its sides. 5 is the hypothenus. then sub the values into the expressions. you will find that sina sinb=cosa cosb.
 

1. What is trigonometry?

Trigonometry is a branch of mathematics that deals with the study of triangles and the relationships between their sides and angles.

2. What are the different products of sine and cosine?

The different products of sine and cosine include the sine of an angle multiplied by the cosine of the same angle (sin x * cos x), the sine of an angle multiplied by the sine of the same angle (sin x * sin x), and the cosine of an angle multiplied by the cosine of the same angle (cos x * cos x).

3. How are these products useful in trigonometry?

These products are useful in trigonometry because they can help solve problems involving trigonometric identities and equations. They also play a key role in the applications of trigonometry in fields such as physics, engineering, and astronomy.

4. Can you give an example of a problem involving products of sine and cosine?

One example of a problem involving products of sine and cosine is finding the value of sin x * cos x given that sin x = 3/5 and cos x = 4/5. To solve this problem, we can use the identity sin x * cos x = (1/2) * sin 2x. Substituting the given values, we get sin 2x = (3/5)(4/5) = 12/25. Then, we can use the double angle formula sin 2x = 2sin x * cos x to find the value of sin x * cos x = (12/25)/2 = 6/25.

5. Are there any other important trigonometric identities involving products of sine and cosine?

Yes, there are several other important trigonometric identities involving products of sine and cosine, such as the double angle formula for cosine (cos 2x = cos^2 x - sin^2 x) and the half angle formulas for sine and cosine (sin (x/2) = ± √[(1 - cos x)/2] and cos (x/2) = ± √[(1 + cos x)/2]). These identities are frequently used in trigonometric calculations and problem-solving.

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