Question

what should be added a2+ab+b2 to obtain 2a2 +3ab​

Answer 1

Just subtract $\sf{a^2+ab+b^2}$ from $\sf{2a^2+3ab}.$ And we get the answer,

$\sf{(2a^2+3ab)-(a^2+ab+b^2)=\underline {\underline {a^2+2ab-b^2}}}$