mathslover
Basic trigonometry help needed.



This Question is Closed

mathslover
Best Response
You've already chosen the best response.
1
Prove : \(\sin (90  \theta) = \cos \theta\)

mathslover
Best Response
You've already chosen the best response.
1
Actually I am confused that how can I : prove that sin in 2nd quadrant is +ve ? That is my basic confusion ...

hartnn
Best Response
You've already chosen the best response.
8
can u use sin (AB) formula?

mathslover
Best Response
You've already chosen the best response.
1
No idea. Actually that was just in start and the formula arises later, so I think that there must be an easier method?

hartnn
Best Response
You've already chosen the best response.
8
draw a right triangle

mathslover
Best Response
You've already chosen the best response.
1
:( not so good but OK ? :)

mathslover
Best Response
You've already chosen the best response.
1
dw:1350046739720:dw nothing is there without naming , OK now I think.

hartnn
Best Response
You've already chosen the best response.
8
dw:1350046691525:dw
now find sin 90theta and cos theta using basic defination

mathslover
Best Response
You've already chosen the best response.
1
OK wait please !

mathslover
Best Response
You've already chosen the best response.
1
In case of sin 90  theta , will perpendicular be : adjacent (base) and base will be opposite?

hartnn
Best Response
You've already chosen the best response.
8
know the basic defination of sin and cos ?
dw:1350046897401:dw
apply it here, in terms of a and b,c

mathslover
Best Response
You've already chosen the best response.
1
OH IT IS soh cah toa and not soa cah toa , sorry :(

mathslover
Best Response
You've already chosen the best response.
1
sin = opposite / hypotenuse
cos = adjacent / hypotenuse

hartnn
Best Response
You've already chosen the best response.
8
yup

mathslover
Best Response
You've already chosen the best response.
1
sin (90theta) = b/c
cos (theta) = b/c
and hence sin(90theta) = cos(theta) , got it now? lol jk. Well is this right @hartnn

hartnn
Best Response
You've already chosen the best response.
8
yep, hence proved.

hartnn
Best Response
You've already chosen the best response.
8
next identity please.

mathslover
Best Response
You've already chosen the best response.
1
prove that sin in 2nd quadrant is +ve ? That is my basic confusion ...

hartnn
Best Response
You've already chosen the best response.
8
here, put theta = theta

hartnn
Best Response
You've already chosen the best response.
8
and use cos(theta) = cos theta

mathslover
Best Response
You've already chosen the best response.
1
how to prove that cos(theta)=theta ?

mathslover
Best Response
You've already chosen the best response.
1
again with the use of right triangle @hartnn ?

hartnn
Best Response
You've already chosen the best response.
8
how will u find theta in triangle ?

mathslover
Best Response
You've already chosen the best response.
1
oh yes .. silly me . So, a cartesian plane ?

mathslover
Best Response
You've already chosen the best response.
1
no, cartesian plane will not work also.

sara12345
Best Response
You've already chosen the best response.
1
ccw : +ve angle
cw : ve angle

hartnn
Best Response
You've already chosen the best response.
8
because lengths will be positive , so ratio will always come out to be positive, hence, maybe cartesian plane won't work

mathslover
Best Response
You've already chosen the best response.
1
Some how agreed .


hartnn
Best Response
You've already chosen the best response.
8
yes, its correct....we could prove it using coordinates.... (cos t,sin t)= (x,y)
so sin t is +ve in 2nd quadrant

mathslover
Best Response
You've already chosen the best response.
1
doubts ended :) thanks a lo.

mathslover
Best Response
You've already chosen the best response.
1
*ton/lot.

hartnn
Best Response
You've already chosen the best response.
8
mathisfun is always a nice reference....

sara12345
Best Response
You've already chosen the best response.
1
more we knw more confuse we become

hartnn
Best Response
You've already chosen the best response.
8
more we practice, more the confusion vanishes....

sara12345
Best Response
You've already chosen the best response.
1
more we practice, more ways we look at things n hence more confusions which ofcourse gives kick ;p