Question

Find the value:-
where a+b=8
and. ab=15

Answer 1

the answer is 3+5=8
(3)(5)=15
so a= 3 and b= 5

Answer 2

By hit and trial we get 3 & 5
and by solving
a+b=8=>a2+2ab+b2=64.(i)
ab=15=>4ab=60.(ii)

Subtracting (ii) from (i), 
a2-2ab+b2=4=>a-b=±2(iii)
From (iii), we get:
a-b=2(iv)&a-b=-2(v)
From (i),a+b=8.
From(iv),a-b=2
Adding them we get,
2a=10=>a=5.(vi)
From (i)&(vi), we get
5+b=8=>b=3
So, first set(a,b)=(5,3)
Now, from(v) a-b=-2
Adding(i)&(v),
2a=6=>a=3(vii)
From(i)&(vii), we get
3+b=8=>b=5.
So,(a,b)=(3,5)

Therefore (a,b)=(5,3)&(3,5)

hope it helps u!!☺