Mathemagic help anyone? (1 Viewer)

[minushuman]

Cause i'm stupid and have no fucking idea whats going on in class i'm pretty stumped at some of teh questions which will be in our exam on monday. Yes it is prelim stuff, yes our school is slow, yes i should pay more attention, especially considering i do 4unit

Anyway, its sum and difference work the sin(a+b) stuff.

If you've got the infocus books, its book1, excercise 6.17 question 11.
If sinx=3/5 and cosy=5/13 find the value of
cosx, siny, sin(x-y), tany, tan(x+y)

If someone wants to explain how to do any of those i'd much appreciate it. Pretty sure u'll only need to do one, i'm not totally brain dead but the textbook sorta doesn't say anything about this stuff. It will do one or two easy examples then go on to ask questions a decent degree harder without anything in the way of explanation or hint.

Cheers.

 

[physician]

Cause i'm stupid and have no fucking idea whats going on in class i'm pretty stumped at some of teh questions which will be in our exam on monday. Yes it is prelim stuff, yes our school is slow, yes i should pay more attention, especially considering i do 4unit

Anyway, its sum and difference work the sin(a+b) stuff.

If you've got the infocus books, its book1, excercise 6.17 question 11.
If sinx=3/5 and cosy=5/13 find the value of
cosx, siny, sin(x-y), tany, tan(x+y)

If someone wants to explain how to do any of those i'd much appreciate it. Pretty sure u'll only need to do one, i'm not totally brain dead but the textbook sorta doesn't say anything about this stuff. It will do one or two easy examples then go on to ask questions a decent degree harder without anything in the way of explanation or hint.

Cheers.

cosx = 4/5 (draw up triangle simple SOH CAH TOA using sinx = 3/5)...
siny = same as above except use ( cosy=5/13)....
tany = same as above use (cosy = 5/13)

sin (x-y) = sinxcosy - cosxsiny, (u've allready found values just sub them in)
tan (x+y) = (tanx+tany) / 1-tanxtany (ur gonna have to find tan x also using sinx = 3/5 draw triangle)...and just sub in values...

 

[|Axis_]

Or if you don't like drawing,

1. cos(x) = sqrt(square(cos(x))) = sqrt(1 - square(sin(x)))

2. sin(y) = ... (Use above technique)

3. sin(x-y) = sin(x)cos(-y) + cos(x)sin(-y) = sin(x)cos(y) - cos(x)sin(y) ... and use the given values and 1. and 2.

4. tan(y) = sin(y)/cos(y)

5. tan(x+y) = [tan(x) + tan(y)] / [1 - tan(x)tan(y)] ... where tan(x) = sin(x)/cos(x)

 

[minushuman]

Thanks a bunch ay. Cheers guys, you've been an awesome help

 

[physician]

ur welcome....

 

[Xayma]

cosx = 4/5 (draw up triangle simple SOH CAH TOA using sinx = 3/5)...
siny = same as above except use ( cosy=5/13)....
tany = same as above use (cosy = 5/13)

sin (x-y) = sinxcosy - cosxsiny, (u've allready found values just sub them in)
tan (x+y) = (tanx+tany) / 1-tanxtany (ur gonna have to find tan x also using sinx = 3/5 draw triangle)...and just sub in values...

You forgot that cos x can also equal -4/5. If it happened to be in the second quadrant.