Question

1)What should be taken away from
$3x^{2} - 4y^{2} + 5xy + 20$
to obtain
$- x^{2} - y^{2} + 6xy + 20$

Answer 1

3x2 − 4y2 + 5xy + 20) − p = − x2 − y2 + 6xy + 20

p = (3x2 − 4y2 + 5xy + 20) − (− x2 − y2 + 6xy + 20)

= 3x2 − 4y2 + 5xy + 20 + x2 + y2 − 6xy − 20

= 3x2 + x2 − 4y2 + y2 + 5xy − 6xy + 20 − 20

= 4x2 − 3y2 − xy