Toán Lớp 8: Tính: a) (x-1)^2 b) (x-1)^2 -(x-3)^2 c) 9x^2-25y^4 d) 49x^2y^6-91y^2 e) x^2-(1+5x)^2 f) (3x-8)^2-(1-2x)^2

Question

Toán Lớp 8:  Tính:  a) (x-1)^2 b) (x-1)^2 -(x-3)^2 c) 9x^2-25y^4 d) 49x^2y^6-91y^2 e) x^2-(1+5x)^2 f) (3x-8)^2-(1-2x)^2

bichhhathu · Answer

text{Giải đáp+Lời giải và giải thích chi tiết::}   a)(x-1)^2=x^2-2x+1   b)(x-1)^2-(x-3)^2=(x-1-x+3)(x-1+x-3)=2(2x-4)=4x-8   c)9x^2-25y^4=(3x)^2-(5y^2)^2=(3x-5y^2)(3x+5y^2)   d)49x^2y^6-91y^2=(7xy^3)^2-(8y)^2=(7xy^3-8y)(7xy^3+8y)   e)x^2-(1+5x)^2=(x+1+5x)(x-1-5x)=(6x+1)(-4x-1)   f)(3x-8)^2-(1-2x)^2=(3x-8-1+2x)(3x-8+1-2x)=(5x-9)(x-7)

kimnguenoanh · Answer

a) ( x - 1 )&sup2; = x&sup2; - 2.x.6 + 6x&sup2;                       = x&sup2; - 12x + 36     b) ( x - 1 )&sup2; - ( x - 3 )&sup2; = [( x - 1 ) + ( x - 3 )] . [( x - 1 ) - ( x - 3 )]                                       = [ x - 1 + x - 3 ].[ x - 1 - x + 3 ]                                       = ( 2x - 4 ) . 2                                       = 4. ( x - 2 )     c) 9x&sup2; - 25y^4 = ( 3x )&sup2; - ( 5y&sup2; )&sup2;                            = ( 3x + 5y&sup2; ). ( 3x - 5y&sup2; )     d) 49x&sup2;y^6 - 91y&sup2; = (7xy&sup3;)&sup2; - (&radic;91.y )&sup2;                                  = ( 7xy&sup3; + &radic;91.y ) . ( 7xy&sup3; - &radic;91.y )     e) x&sup2; - ( 1 + 5x )&sup2; = [ x + ( 1 +5x )] . [ x - ( 1+ 5x )]                                = ( x + 1 + 5x ).( x - 1 - 5x )                                = ( 6x+1 ). ( -4x - 1)     f) ( 3x - 8 )&sup2; - ( 1-2x )&sup2; = [( 3x - 8 ) + ( 1- 2x)] . [(3x - 8) - ( 1 - 2x )]                                        = ( 3x- 8 + 1 - 2x ) . ( 3x - 8 - 1 + 2x )                                        = ( 1x - 7 ). ( 5x - 9 )      Cj tr&igrave;nh b&agrave;y chi tiết gi&uacute;p e nhen, đọc chỗ n&agrave;o ko hiểu cứ hỏi cj !        ~HỌCTỐT~ Na ~