What is obtained after simplifying (6x^2-4xy+y^2-(2x^2+5xy-3y^2))?

Correct answer: \(4x^2-9xy+4y^2\)

A minus sign precedes the second bracket, so the sign of every term inside it changes: \(6x^2-4xy+y^2-2x^2-5xy+3y^2\). Combining like terms gives \((6-2)x^2=4x^2\), \((-4-5)xy=-9xy\), and \((1+3)y^2=4y^2\). Hence, the simplified expression is \(4x^2-9xy+4y^2\). In option D, the sign of the \(y^2\) term is incorrect. Exam tip: when subtracting a bracket, change the sign of every term in that bracket before combining like terms.