c^2 = a^2 + b^2 - 2*ab*Cos(C)
c = 16; a = 17; b = 8 (what you call a and b don't really matter. c does). Substitute.
16^2 = 17^2 + 8^2 - 2*17*8*Cos(C) Add the first 2 on the right.
256 = 289 + 64 - 282*cos(C)
256 = 353 - 282*cos(C)
Whatever you do, don't do any more combing on the right side. Subtract 353 from both sides.
-97 = -282 * cos(C )
Divide by 282
0.34397 = cos(C)
cos-1(0.34397) = C ; C = 69.88 degrees.
Do you need more help on this question? All of these are done the same way.
Given
Elysse paid for her sandwich and drink with a $10 bill and received $0.63 in change.
The sandwich cost $7.75 and sales tax was $0.47.
Find out the cost of her drink
To proof
Let the cost of her drink be x.
As given in the question
Elysse paid for her sandwich and drink with a $10 bill and received $0.63 in change.
Elysse paid for her sandwich and drink = 10 - 0.63
= $ 9.37
sandwich cost $7.75 and sales tax was $0.47
Than the equation becomes
x = 9.37 - (7.75 + 0.47)
x = 9.37 - 8.22
x = $ 1.15
The cost of the drink is $ 1.15.
Hence proved
in a right-triangle, like in the 1st Quadrant, cosine and sine are complements, so then
sin(x) = cos(90° - x)
cos(x) = sin(90° - x)
for this case, sin(<u>90°</u>) = cos(90° - <u>90°</u>), or just cos(0°) = 1.
