Simplify 15a^2-6ab-8a^2+20-5ab-31+a^2-ab

$15 a^{2} - 6 a b - 8 a^{2} + 20 - 5 a b - 31 + a^{2} - a b$

Subtract $8 a^{2}$ from $15 a^{2}$ .

$7 a^{2} - 6 a b + 20 - 5 a b - 31 + a^{2} - a b$

Add $7 a^{2}$ and $a^{2}$ .

$8 a^{2} - 6 a b + 20 - 5 a b - 31 - a b$

Subtract $5 a b$ from $- 6 a b$ .

$8 a^{2} - 11 a b + 20 - 31 - a b$

Subtract $a b$ from $- 11 a b$ .

$8 a^{2} - 12 a b + 20 - 31$

Subtract $31$ from $20$ .

$8 a^{2} - 12 a b - 11$