Toán Lớp 7: BÀI 1: thực hiện phép tính a) (3x+1)^2 b) (x-3/4)^2 c) (3x-1).(3x+1) d) (2x^2-1/2y)^2 e) (xy^2+1).(xy^2-1) f) (x+y)^2.(x-y)^2 * giúp

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Toán Lớp 7:  BÀI 1: thực hiện phép tính  a) (3x+1)^2  b) (x-3/4)^2 c) (3x-1).(3x+1) d) (2x^2-1/2y)^2 e) (xy^2+1).(xy^2-1) f) (x+y)^2.(x-y)^2  * giúp iêm =))

thucquyenlan · Answer

Giải đáp:       Lời giải và giải thích chi tiết:    a) (3x+1)^2 =(3x)&sup2;+2.3x +1=9x&sup2;+6x+1     b) (x-3/4)^2 =x&sup2;-2.x.3/4 +(3/4)&sup2; =x&sup2;-3x/2 +9/16     c) (3x-1).(3x+1)=(3x)&sup2;-1=9x&sup2;-1     d) (2x^2-1/2y)^2=(2x&sup2;)&sup2;-2.2x&sup2;.1/2 y +(1/2 y)&sup2; = 4x^4 -2x&sup2;y +y&sup2;/4     e) (xy^2+1).(xy^2-1) =(xy&sup2;)&sup2;-1 =x&sup2;y^4 -1     f) (x+y)^2.(x-y)^2 = [(x+y)(x-y ) ]&sup2; =(x&sup2;-y&sup2;)&sup2; =(x&sup2;)&sup2;-2x&sup2;.y&sup2;+(y&sup2;)&sup2; =x^4 -2x&sup2;y&sup2;+y^4

ngocle44 · Answer

Giải đáp:       Lời giải và giải thích chi tiết:    a) $(3x+1)^2 =(3x)&sup2;+2.3x +1=9x&sup2;+6x+1$     b) (x-3/4)^2=$x&sup2;-2.x.$3/4 +(3/4)&sup2; =x&sup2;- (3x)/2 +9/16     c)     $(3x-1)(3x+1)$    $=(3x)&sup2;-1=9x&sup2;-1$    d)    (2x^2-1/(2y))^2   =$(2x&sup2;)&sup2;-2.2x&sup2;$.1/(2 y) +(1/(2 y))&sup2;   = $4x^4 -2x&sup2;y +$(y&sup2;)/4   e) $(xy^2+1).(xy^2-1)$   $=(xy&sup2;)&sup2;-1$   $=x&sup2;y^4 -1$    f)      $ (x+y)^2.(x-y)^2$     $= [(x+y)(x-y ) ]&sup2;$     $=(x&sup2;-y&sup2;)&sup2; =(x&sup2;)&sup2;-2x&sup2;.y&sup2;+(y&sup2;)&sup2;$     $=x^4 -2x&sup2;y&sup2;+y^4$