Subtract$\displaystyle 1 / 2[12y^2 + 1 / 4x(16x-8y)]$from$\displaystyle 12y^2 + 7xy + 5x^2$

And this is how I done it...

$\displaystyle 12y^2 + 7xy + 5x^2 - 1/2[12y^2 - 1/4x(16x + 8y)]$

$\displaystyle = 12y^2 + 7xy + 5x^2 - 6y^2 - 2y + 2xy$

$\displaystyle = 6y^2 + 8xy + 5x^2 - 2x$

However, it turns out wrong. If you could point out my mistake while solving this sum, I would appreciate your kindness. Thank you!