Finding exact values for the tangent of the sum or difference of two angles is a little more complicated, but again, it is a matter of recognizing the pattern.
Finding the sum of two angles formula for tangent involves taking quotient of the sum formulas for sine and cosine and simplifying. Recall,
Let’s derive the sum formula for tangent.
We can derive the difference formula for tangent in a similar way.
Sum and difference formulas for tangent
The
sum and difference formulas for tangent are:
Given two angles, find the tangent of the sum of the angles.
Write the sum formula for tangent.
Substitute the given angles into the formula.
Simplify.
Finding the exact value of an expression involving tangent
Find the exact value of
Let’s first write the sum formula for tangent and then substitute the given angles into the formula.
Next, we determine the individual function values within the formula:
We can use the sum and difference formulas to identify the sum or difference of angles when the ratio of sine, cosine, or tangent is provided for each of the individual angles. To do so, we construct what is called a reference triangle to help find each component of the sum and difference formulas.
To find
we begin with
and
The side opposite
has length 3, the hypotenuse has length 5, and
is in the first quadrant. See
[link] . Using the Pythagorean Theorem, we can find the length of side
Since
and
the side adjacent to
is
the hypotenuse is 13, and
is in the third quadrant. See
[link] . Again, using the Pythagorean Theorem, we have
Since
is in the third quadrant,
The next step is finding the cosine of
and the sine of
The cosine of
is the adjacent side over the hypotenuse. We can find it from the triangle in
[link] :
We can also find the sine of
from the triangle in
[link] , as opposite side over the hypotenuse:
Now we are ready to evaluate
We can find
in a similar manner. We substitute the values according to the formula.
For
if
and
then
If
and
then
Then,
To find
we have the values we need. We can substitute them in and evaluate.
t he silly nut company makes two mixtures of nuts: mixture a and mixture b. a pound of mixture a contains 12 oz of peanuts, 3 oz of almonds and 1 oz of cashews and sells for $4. a pound of mixture b contains 12 oz of peanuts, 2 oz of almonds and 2 oz of cashews and sells for $5. the company has 1080
Lairene and Mae are joking that their combined ages equal Sam’s age. If Lairene is twice Mae’s age and Sam is 69 yrs old, what are Lairene’s and Mae’s ages?