1. Warm-up 8/22 Verify that the equation is an identity.
sin x tan x = sec x – cos x
1 = tan x cos x csc x
Find a numerical value of one trig function
3. cos x csc x = 1

2. 2.3 Sum and difference identities

5. Ex: Use the sum or difference identity to find the exact value of tan 735°
Subtract 360 until you find the angle
between 0 and 360
Express the angle using known angles
(special triangles, unit circle)
Use the identity
Evaluate each trig value
Get c.d.
Mult by recip.
rationalize
Finished on next slide

6. Ex continued
distribute
Combine like terms, simplify

7. Ex: find exact value for
You can change to degrees, if that is easier to work with
Plug into formula for sinq, you will flip at the end.
(sin45)(cos30)+(cos45)(sin30)
This is sinq so flip to get cscq
Can’t have radicals in denominator so mult numerator and denominator by

8. Ex. Find the EXACT value of sin(x + y) if
, sin x = , and sin y =
Means we are in QUAD I
Write formula: sinx cosy + cosx siny
Plug in what we know:
Draw triangles to find what we don’t know 7 13
x2+72=132 9 17
x2+92=172 y x

9. Ex. Verify the identity. Use the reciprocal identity.
Use the sum of sines identity.
Evaluate trig functions.
Simplify.
Done!

10. 2.3 Assignment
p. 442 #15 – 41 odds SHOW WORK