Can anyone please help me in this math?

Let x be the number of books and y the price per book.

xy = 132 ⇒ y = 132/x

(x - 1)(y + 1) = 132

xy + x - y - 1 = 13.2

k

xy = 132, soooo

x - y = 1

x - 132/x = 1

x² - x - 132 = 0

(x + 11)(x - 12) = 0 ⇒ x ∈ {-11, 12}

Discard the negative root

y = 11, xy = (12)(11) = 132

(x - 1)(y + 1) = (11)(12) = 132 ✓

Sold x books at unit price (132/x). Selling (x-1) books at unit price [1+(132/x)] gets him 132 so (x-1)[1+(132/x)]

= 132, ie., (x-1) + 132(x-1)/x = 132, ie., x(x-1) +132(x-1) - 132x = 0, ie., x^2 - x - 132 =0, ie.,(x-12)(x+11) = 0,

ie., x = 12. { require x > 0}

money he got by selling x books at $132 = 132x (in dollars)

money he would have got by selling x-1 books at $133 = 133(x-1) (in dollars)

now money both cases are same. so

132x = 133(x - 1)

132 x = 133x - 133

132x - 133x = -133 .. .. .. // when -133x taken to other side, its sign changed

-x = -133

x = 133