Question

what must be subtracted from a³b+6a²b²-7ab+4 to get -7a²b²+2a³b+6ab-1

Answer 1

${a}^{3}b + 6 {a}^{2}b - 7ab + 4 - ( - {a}^{3} + 13 {a}^{2}{b}^{2} - 13ab + 5) \\ = {a}^{3}b + 6 {a}^{2}b - 7ab + 4 + {a}^{3}b - 13 {a}^{2}{b}^{2} + 13ab - 5 \\ = - 7 {a}^{2} {b}^{2} + 2 {a}^{3} b + 6ab - 1$