Question

3. Simplify (4x2 - 2xy + 3y2 - 4) + (4xy - 3x2 - y2 - 2) - (x2 + xy - 4y? - 3) and find the value of the result, given x = -15 and y = 5.​

Answer 1

$(4 {x}^{2} - 2xy + 3y {y}^{2} - 4) \\ + (4xy - 3 {x}^{2} - {y}^{2} - 2) \\ - ( {x}^{2} + xy - 4{y}^{2} - 3)$

$= 4 {x}^{2} - 2xy + 3 {y}^{2} - 4 + 4xy - 3 {x}^{2} - {y}^{2} - 2 - {x}^{2} - xy + 4 {y}^{2} + 3$

$= 8 {y}^{2} + xy - 3$

Putting in their values,

$= 8 {(5)}^{2} + ( - 15)(5) - 5$

$= 200 - 75 - 5$

$= 120$