well by replacing sinx and cosx with their values in t (cbf typing this up) you end up with:
2tb + a(1-t^2) = c(1+t^2)
expand and rearange this you get:
(c+a)t^2 -2bt +c -a = 0
there for for it to have real roots discriminant >o
4b^2 -4(c-a)(c+a)>=0
4b^2 + 4a^2 >=4c^2
b^2 + a^2 >= c^2
new...
cos^2x = 2cos^2(x/2)
-cos^2x = -2cos^2(x/2)
1-cos^2x= 1-2cos^2(x/2)
1-cos^2x=cosx
cos^2x + cosx -1=0
cosx = -1/2plus or minus sqrt(5)/2
try that and see if you get the answer=S
i) ok i formed the equation with roots 1/alpha etc so it becomes:
rx^3 + qx^2 + px + 1= 0
then since the roots are 1/alpha + 1 /beta + 1/gamma and they are in arithmatic seq. then they can be written as :
1/beta - d , 1/beta , 1/beta + d
then sum of roots = -q /r
1/beta -d + 1/beta + 1/beta...
ok, generally, when your given a question show that the integral between -1->1 of f(x) dx is = 0 you would use f(-x) = -f(x) to show that its an odd function and then you can say that the integral of an odd function between limits -a -> a is equal to 0.
but, in the case of sinx it's not...
you cannot use f(-x) = -f(x) for sinx since you need to use the fact that it is an odd function to prove that.
and even function is symmetrical about the y-axis an odd function has POINT symmetry about the origin
well i know as a fact that y= 2sinx is odd but to show it, you use the graph and show it has point symmetry about the origin. and the integral of an odd function with limits a->-a is 0