Question

what should be subtracted from 3a²-4b²+5ab to obtain -a²-b²+6ab

Answer 1

3a²-4b²+5ab-x(let)=-a²-b²+6ab
Now, we will transpose, x on the right side and -a²-b²+6ab on the left side.
We will get=  3a²-4b²+5ab+a²-b²+6ab=x
3a²+a²=4a²
-4b²-b²=-5b²
5ab+6ab=11abSo, the answer is4a²-5b²+11ab

Answer 2

Let the expression to be subtracted be equal to X. It contains terms a², b², and ab.

$3 a^2 - 4 b^2 + 5 a b - X = - a^2 - b^2 + 6 a b$

Take X to the right side, and Bring the expression on the right to the left side of equal to.

$3 a^2 - 4 b^2 + 5 a b + a^2 + b^2 - 6 a b = X$

Add the similar terms

$(3+1)a^2 + (-4+1)b^2 + (5-6) ab = X \\ \\ 4 a^2 -3b^2 -ab = X, OR,\ \ \ \ \ \ X = 4a^2 - 3 b^2 - ab$