SUM AND DIFFERENCE FORMULAS

PRIOR KNOWLEDGE

• Sine=opp/Hyp
• Cosine=Adj/Hyp
• Tangent=Opp/Adj
• Unit circle

INTERPRET THE RULES

• Cosine(A+-B)=CosACosB+-SinASinB
• Sine(A+-B)=SinACosB+-CosASinB

ESSENTIAL QUESTION

• How does the sum & difference formula help you find the value of trig expression such as sine & cosine

Stacy and Susan are both picking up large rocks.

• 45*

30*

Stacy is picking up the rock at an angle of 30*
Susan is picking up the rock at an angle of 45*

By using the sum and difference formula you can find the exact value of the force being used by both girls combined.

Find
Sin (7π/6 + π/4)
*you can't add these formulas like this the sum and difference formula must be used
You find these numbers on the unit circle

Plug in numbers into formulas

Sin(7π/6)Cos(π/4) + Cos(7π/4)Sin(π/4)

Use coordinates from the the unit circle
(1/2)(√2/2) + (√3/2)(√2/2)

-√2/4 + -√6/4
=
√2 - √6/4