a)
A= -7x2 - 3y2 + 9xy - 2x2 + y2
= (-7x2 - 2x2) + (-3y2 + y2) + 9xy
= -9x2 - 2y2 + 9xy
B= 5x2 + xy - x2 - 2y2
= (5x2 - x2) - 2y2 + xy
= 4x2 - 2y2 + xy
b)
C= A +B = (-9x2 - 2y2 + 9xy) + (4x2 - 2y2 + xy)
= -9x2 - 2y2 + 9xy + 4x2 -2y2 + xy
= (-9x2 + 4x2) + (-2y2 -2y2) + (9xy + xy)
C = -5x2 -4y2 +10xy
a) \(A=-7x^2-3y^2+9xy-2x^2+y^2\)
\(\Leftrightarrow A=\left(-7x^2-2x^2\right)-\left(3y^2-y^2\right)+9xy\)
\(\Leftrightarrow A=-9x^2-2y^2+9xy\)
\(B=5x^2+xy-x^2-2y^2\)
\(\Leftrightarrow B=\left(5x^2-x^2\right)-2y^2+xy\)
\(\Leftrightarrow B=4x^2-2y^2+xy\)
b) \(C=A+B\)
\(\Leftrightarrow C=-9x^2-2y^2+9xy+4x^2-2y^2+xy\)
\(\Leftrightarrow C=\left(-9x^2+4x^2\right)-\left(2y^2+2y^2\right)+\left(9xy+xy\right)\)
\(\Leftrightarrow C=-5x^2-4y^2+10xy\)
a,
A= -7x2 - 3y2 + 9xy - 2x2 + y2
= ( -7x2 - 2x2 ) + ( -3y2 + y2 ) + 9xy
= -9x2 - 2y2 + 9xy
B= 5x2 + xy - x2 - 2y2
= ( 5x2 - x2 ) + xy - 2y2
= 4x2 + xy - 2y2
b,
A+B= ( -9x2-2y2+9xy )+( 4x2+xy-2y2 )
= -9x2 - 2y2 + 9xy + 4x2 + xy - 2y2
= ( -9x2+4x2 )+( -2y2-2y2 )+(9xy+xy )
= -5x2 - 4y2 + 10xy
Vậy C= -5x2 -4y2 + 10xy
