Toán Lớp 7: Bài 1: Rút gọn biểu thức a,A=(x-y).( x ²+xy+y ² )-(x +y).(x ²-xy+y ²)

Question

Toán Lớp 7:  Bài 1: Rút gọn biểu thức a,A=(x-y).( x ²+xy+y ² )-(x +y).(x ²-xy+y ²)

mytamhoang · Answer

a) Ta c&oacute; :   A = (x - y)(x^2 + xy + y^2) - (x+y)(x^2 -xy+y^2)   A = (x^3 - y^3) - (x^3 + y^3)   A = x^3 - y^3 - x^3 - y^3   A = -2y^3

khanhngantoan · Answer

a) C&aacute;ch 1 : Sử dụng hằng đẳng thức ( Lớp 8 )      A = ( x - y )( x&sup2; + xy + y&sup2; ) -  ( x + y )( x &sup2;- xy + y &sup2; )     A = x&sup3; - y&sup3; - ( x&sup3; + y&sup3; ) * &Aacute;p dụng hằng đẳng thức số 6 , 7 *     A = x&sup3; - y&sup3; - x&sup3; - y&sup3;     A = -2y&sup3;       C&aacute;ch 2 : Ph&aacute; ngoặc trực tiếp      A = ( x - y )( x&sup2; + xy + y&sup2; ) - ( x + y )( x &sup2;- xy + y &sup2; )     A = x . ( x&sup2; + xy + y&sup2; ) - y . ( x&sup2; + xy + y&sup2; ) - x .   ( x &sup2;- xy + y &sup2; ) - y .   ( x &sup2;- xy + y &sup2; )     A = x&sup3; + x&sup2;y + xy&sup2; - x&sup2;y - xy&sup2; - y&sup3; - x&sup3; + x&sup2;y - xy&sup2; - x&sup2;y + xy&sup2; - y&sup3;     A = ( x&sup3; - x&sup3; ) ( - y&sup3; - y&sup3; ) + ( x&sup2;y - x&sup2;y + x&sup2;y - x&sup2;y ) + ( xy&sup2; - xy&sup2; - xy&sup2; + xy&sup2; )     A = -2y&sup3;