u. s. p. srinivas aditya
Last Activity: 13 Years ago
sqrt{a-b/a+b}=tanAtanB (given)
multiplying and dividing (a-b) in LHS...
sqrt{(a-b)(a-b)/(a+b)(a-b)}=tanAtanB
sqrt{(a-b)^2/a^2-b^2}=tanAtanB
squaring both sides...
(a-b)^2/a^2-b^2=tan^2Atan^2B
a^2-b^2=(a-b)^2/tan^2Atan^2B ~eq.[1]
To prove: (a-bCos2A)(a-bCos2B)=a^2-b^2
from eq.[1]
we can prove, (a-b)^2/tan^2Atan^2B=(a-bCos2A)(a-bCos2B)
RHS-
=> {a-b[(1-tan^2A)/(1+tan^2A)]}{a-b[(1-tan^2B)/(1+tan^2B)]}
=> [a-(b-btan^2A)/(1+tan^2A)][a-(b-btan^2B)/(1+tan^2B)]
=> [(a+atan^2A-b+btan^2A)(a+atan^2B-b+btan^2B)]/[1+tan^2A+tan^2B+tan^2Atan^2B]
on solving further....
=> (a^2+b^2-2ab)(tan^2B)/(tan^2Atan^4B)
=> (a-b)^2/tan^2Atan^2B
hence proved...!!