# sinx+cosx=0 for 0<x<360Watch

#1
how do i do this? i keep getting it wrong? what error have i made in my working?

sinx + cosx = 0 i applied the tanx = sinx/cosx identity so i divided by cosx

tanx + 1 =0
tanx = -1
x = arctan(-1) =-45

then i got theta = 45 and 225

but the book says it is 135 and 315.
0
7 years ago
#2
The period of the tan graph is 180.
So you get other solutions by adding or subtracting multiples of 180 to your principal value of -45.
1
7 years ago
#3
You found that so why did you deduce that is a solution?

Note that , so you need to add 180 a few times to get all the solutions in the given range.
#4
(Original post by nuodai)
You found that so why did you deduce that is a solution?

Note that , so you need to add 180 a few times to get all the solutions in the given range.
i don't know >.> i was thinking about symmetry
0
7 years ago
#5
(Original post by NewCrack)
i don't know >.> i was thinking about symmetry
I see. That only works for , since ; but for or we have so it doesn't work.
7 years ago
#6
nah dude tan has rotational symetry. so you have to add and subtract 180 to ur orriginal answer untill you get all the answerr within the given range
0
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