eg no-5 chapter 4 ,lesson 3,it is given that (x + 3) (y – 1) = xy – 15
x (y – 1) + 3 (y – 1) = xy – 15
xy – x + 3y – 3 = xy – 15
– x + 3y – 3 = – 15
∴ x – 3y = 12
but shouldnt the ans have been x+3y=12.
– x + 3y – 3 = – 15
⇒ -1(– x + 3y – 3) = -1(– 15)
⇒ x – 3y + 3 = 15
⇒ x – 3y = 15 - 3 = 12