11.put x=0,y=0.it satisfies the given cond.
so the ans is 0.
1) If sin x + sin y = 3(cos y - cos x), then find the value of sin3x + sin3y ?
2) If sin (x/2) + cos (x/2) = -1/2 , 3pie/2 < x < 2pie, then the value of sin2x?
-
UP 0 DOWN 0 1 14
14 Answers
1Hey anyone there ready to help me??
Guys solve it.... i've tried it but is not gettin the correct answer. Please also write the steps.
1My answer is coming out to be 0 for sin3x+sin3y. Is it right ? If yes then i can give the explanation.
62Rahul but that does not mean that this expression will be always zero..
be careful in such multiple correct answer questions.....
1sin x+3cos x= 3cos y - sin y
or, √10(1√10sin x + 3√10cos x) = √10(3√10cos y - 1√10sin y)
Let 1√10= cos α
Hence 3√10= sin α
Hence sin(α+x) = sin(α-y)
or, 2 sinx+y2 cos 2α+x-y2 = 0
or, sin x+y2=0
or,x=-y
or,sin3x = -sin 3y
Hence sin 3x+sin 3y = 0.
1there are 2 solutions ...
sin x + sin y=3 (cos y- cos x)
=> 2 sin{(x+y)/2} cos {(x-y)/2}= 6 sin {(x+y)/2} sin {(x-y)/2}
either sin {(x+y)/2}=0 or,tan {(x-y)/2}=1/3
aveek has taken only d first solution....but we have to take also the second solution into account
1maths_psy....wht can u do with the tan function.....how can u bring it to sin when u have a simpler expression before ur eyes ?
1both are answers until d latter is found out to be an extranious root (i,e which dus not satisfy d original solution)...hav to check whether d second 1 is an extranious root or not... we can get value of x and y through general solution.....
1But do u really need to take a step more for an mcq question....when u've already got the answer.....? ne ways ......ur solution is more complete than mine...............:-)
1dont mind aveek....in case of objective paper u would have saved a lot of time......but be carefull the next time onwards in case of multiple correct answers...........
1yes,in case of multiple correct answers u would hav got wrong if u ticked only d 1st 1
1Thanks guys. i too solved the question. And got the answers to both the questions.
However for the 1st question, I only got answer 0.
2nd question has answer -3√7/8