Question

If $a+b=7$ and $ab=12$ find value of $a^2-ab+b^2$.

Answer 1

Let $a+b=7$ and $ab=12$.......(1).

Now

$a^2-ab+b^2$

$=(a+b{)}^2-3ab$

$=7^2-3.12$ [ Using (1)]

$=49-36$

$=13$.