Find the sum of $4x^2+8xy-2y^2$ and $8xy-5y^2+x^2$.

Find the sum of $9x^2-6x+7, 5-4x$ and $6-3x^2$.

Find the sum of $5x^2-2xy+3y^2, -2x^2+5xy+9y^2$ and $3x^2-xy-4y^2$.

Find the sum of $a^2+b^2+2ab, 2b^2+c^2+2bc$ and $4c^2-a^2+2ac$.

Find the sum of $9ax-6bx+8, 4ax+8bx-7$ and $-6ax-4bx-3$.

Find the sum of $abc+2ba+3ac, 4ca-4ab+2bca$ and $2ab-3abc-6ac$.

Find the sum of $4a^2+5b^2-6ab, 3ab, 6a^2-2b^2$ and $4b^2-5ab$.

Find the sum of $x^2+x-2, 2x-3x^2+5$ and $2x^2-5x+7$.

Find the sum of $4x^3+2x^2-x+1, 2x^3-5x^2-3x+6, x^2+8$ and $5x^3-7x$.