Question

if (a+b)=9 ab=20 find the value of a_b

Answer 1

(a+b)²=(a-b)² + 4ab
9 * 9 = (a-b)²+4*20
81 = (a-b)² +80
81 - 80 = (a-b)²
1 = (a-b)²

taking root both the side,
1 = a-b

Answer 2

b=   -5 or -4
a=    14 or 13