NDA2018MathematicsTrigonometric Ratios & IdentitiesActual
If (x+y) (x-y) = a+b a-b , then what is x y equal to?
Options
- Aa b
- Bb a
- Ca+b a-b
- Da-b a+b
Correct answer
A. a b
Step-by-step solution
(x+y) (x-y) = a+b a-b Applying componendo and dividendo, we get aligned & (x+y)+ (x-y) (x+y)- (x-y) = a+b+a-b a+b-a+b & 2 ( x+y+x-y 2 ) ( x+y-x+y 2 ) 2 ( x+y+x-y 2 ) ( x+y-x+y 2 ) = 2 a 2 b & x y x y = a b & x y = a b aligned