Toán Lớp 7: Tính A+B, A-B, B-A
a, A=x ²y+0xy ³-7,5x ³y ²+x ³
B=3xy ³-x ²y+5,5x ³y ²
b, A=x ^5+xy+0,3y ²-2
B=x ²y ³+5+1,3y ²
c, A=x ²y+xy ²-5x ²y ²+x ³
B=3xy ²-x ²y+x ²y ²
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Toán Lớp 7: Tính A+B, A-B, B-A
a, A=x ²y+0xy ³-7,5x ³y ²+x ³
B=3xy ³-x ²y+5,5x ³y ²
b, A=x ^5+xy+0,3y ²-2
B=x ²y ³+5+1,3y ²
c, A=x ²y+xy ²-5x ²y ²+x ³
B=3xy ²-x ²y+x ²y ²
Comments ( 1 )
a)A = {x^2}y + 0.x{y^3} – 7,5{x^3}{y^2} + {x^3}\\
= {x^2}y – 7,5{x^3}{y^2} + {x^3}\\
B = 3x{y^3} – {x^2}y + 5,5{x^3}{y^2}\\
\Leftrightarrow A + B\\
= {x^2}y – 7,5{x^3}{y^2} + {x^3} + 3x{y^3} – {x^2}y + 5,5{x^3}{y^2}\\
= – 2{x^3}{y^2} + {x^3} + 3x{y^3}\\
A – B\\
= {x^2}y – 7,5{x^3}{y^2} + {x^3} – \left( {3x{y^3} – {x^2}y + 5,5{x^3}{y^2}} \right)\\
= {x^2}y – 7,5{x^3}{y^2} + {x^3} – 3x{y^3} + {x^2}y – 5,5{x^3}{y^2}\\
= 2{x^2}y – 13{x^3}{y^2} + {x^3} – 3x{y^3}\\
B – A\\
= 3x{y^3} – {x^2}y + 5,5{x^3}{y^2} – \left( {{x^2}y – 7,5{x^3}{y^2} + {x^3}} \right)\\
= 3x{y^3} – {x^2}y + 5,5{x^3}{y^2} – {x^2}y + 7,5{x^3}{y^2} – {x^3}\\
= 3x{y^3} – 2{x^2}y + 13{x^3}{y^2} – {x^3}\\
b)A = {x^5} + xy + 0,3{y^2} – 2\\
B = {x^2}{y^3} + 5 + 1,3{y^2}\\
A + B\\
= {x^5} + xy + 0,3{y^2} – 2 + {x^2}{y^3} + 5 + 1,3{y^2}\\
= {x^5} + xy + 1,6{y^2} + 3 + {x^2}{y^3}\\
A – B\\
= {x^5} + xy + 0,3{y^2} – 2 – \left( {{x^2}{y^3} + 5 + 1,3{y^2}} \right)\\
= {x^5} + xy + 0,3{y^2} – 2 – {x^2}{y^3} – 5 – 1,3{y^2}\\
= {x^5} + xy – 1{y^2} – 7 – {x^2}{y^3}\\
B – A\\
= {x^2}{y^3} + 5 + 1,3{y^2} – \left( {{x^5} + xy + 0,3{y^2} – 2} \right)\\
= {x^2}{y^3} + 5 + 1,3{y^2} – {x^5} – xy – 0,3{y^2} + 2\\
= {x^2}{y^3} + 7 + 1{y^2} – {x^5} – xy\\
c)A = {x^2}y + x{y^2} – 5{x^2}{y^2} + {x^3}\\
B = 3x{y^2} – {x^2}y + {x^2}{y^2}\\
A + B\\
= {x^2}y + x{y^2} – 5{x^2}{y^2} + {x^3} + 3x{y^2} – {x^2}y + {x^2}{y^2}\\
= 4x{y^2} – 4{x^2}{y^2} + {x^3}\\
A – B\\
= {x^2}y + x{y^2} – 5{x^2}{y^2} + {x^3} – \left( {3x{y^2} – {x^2}y + {x^2}{y^2}} \right)\\
= {x^2}y + x{y^2} – 5{x^2}{y^2} + {x^3} – 3x{y^2} + {x^2}y – {x^2}{y^2}\\
= 2{x^2}y – 2x{y^2} – 6{x^2}{y^2} + {x^3}\\
B – A\\
= 3x{y^2} – {x^2}y + {x^2}{y^2} – \left( {{x^2}y + x{y^2} – 5{x^2}{y^2} + {x^3}} \right)\\
= 3x{y^2} – {x^2}y + {x^2}{y^2} – {x^2}y – x{y^2} + 5{x^2}{y^2} – {x^3}\\
= 2x{y^2} – 2{x^2}y + 6{x^2}{y^2} – {x^3}
\end{array}$