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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Thực hiện phép tính: $b) (6x^{2}- 5)(2x+3)- 12x^{3}- 18x^{2}- 10x-15$

Toán Lớp 8: Thực hiện phép tính:
$b) (6x^{2}- 5)(2x+3)- 12x^{3}- 18x^{2}- 10x-15$

Comments ( 2 )

  1. b) ( 6x^2 – 5 ) ( 2x + 3 ) – 12x^3 – 18x^2 – 10x – 15
    = 6 ( 2x + 3 ) x^2 – 5 ( 2x + 3 ) – 12x^3 – 18x^2 – 10x – 15   ( Dùng phương pháp nhóm hạng tử )
    = 12x^3 + 18x^2 – 10x – 15 – 12x^3 – 18x^2 – 10x – 15
    = 12x^3 + 18x^2 – 10x – 30 – 12x^3 – 18x^2 – 10x
    = 18x^2 – 10x – 30 – 18x^2 – 10x
    = – 20x – 30

  2. $\\$
    Ta sẽ rút gọn :
    (6x^2 -5)(2x+3)
    = 6x^2 (2x+3)-5(2x+3)
    = 12x^3 + 18x^2 – 10x – 15
    (6x^2 – 5)(2x+3)-  12x^3 – 18x^2 – 10x – 15
    = 12x^3 + 18x^2 – 10x – 15 – 12x^3 – 18x^2 – 10x – 15
    = (12x^2 – 12x^3)+(18x^2 – 18x^2)+(-10x – 10x)+(-15-15)
    = -20x – 30
     

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222-9+11+12:2*14+14 = ? ( )

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