1in the options both c) and d) are given
But answer is c)
Why ?
:-(
If x2-2xcosα +1=0 and y2-2ycosβ+1=0
then what is the value of 2cos(α+β)
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4 Answers
341(a) 2
(b) -2
(c) xy + 1/xy
(d) x/y + y/x
Take your pick, any of the above are valid under different conditions (implying that you ought to have mentioned them)
112cosαcosβ-2sinαsinβ=?
x=cosα±√cos2α-11
y=cosβ±√cos2β-11
u shall check
Is x2y2+1=x2+y2?????
It is not So
So book is incorrect[1]