tìm x biết a,16x ²-(4x-5) ²=15 b,(2x+3) ²-4.(x-1).(x+1)=49 c,(2x+1).(1-2x)+(1-2x) ²=18 d,(3x-1) ²-(3x-2) ²=0 mong anh em giúp tôi sẽ vote cho 5 anh sao và cho câu trả lời hay nhất nhớ làm đg

duydung1005

2 năm trước

Loga Sinh Học lớp 12

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1 trả lời

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129529104919705

Lời giải:

`a)`

`16x^(2)-(4x-5)^2=15`

`⇔16x^(2)-16x^(2)+40x-25-15=0`

`⇔40x-40=0`

`⇔x=1`

Vậy `x=1`

`b)`

`(2x+3)^(2)-4(x-1)(x+1)=49`

`⇔4x^(2)+12x+9-4(x^(2)-1)=49`

`⇔4x^(2)+12x+9-4x^(2)+4-49=0`

`⇔12x-36=0`

`⇔x=3`

Vậy `x=3`

`c)`

`(2x+1)(1-2x)+(1-2x)^2=18`

`⇔(1+2x)(1-2x)+(1-2x)^2=18`

`⇔1-4x^(2)+1-4x+4x^(2)-18=0`

`⇔-4x-16=0`

`⇔-4x=16`

`⇔x=-4`

Vậy `x=-4`

`d)`

`(3x-1)^(2)-(3x-2)^2=0`

`⇔(3x-1-3x+2)(3x-1+3x-2)=0`

`⇔-1(6x-3)=0`

`⇔6x-3=0`

`⇔x=1/2`

Vậy `x=1/2`

Áp dụng HĐT số `3` : `a^(2)-b^2=(a-b)(a+b)`

Vote (0) Phản hồi (0) 2 năm trước

tantuyet

`#Sad`

`a)`

`16x^2-(4x-5)^2 = 15`

`⇔ (4x-4x+5)(4x+4x-5) = 15`

`⇔ 5(8x-5) = 15`

`⇔ 40x-25 = 15`

`⇔ 40x = 40`

`⇔ x = 1`

`\text{Vậy S=}` `{1}`

`b)`

`(2x+3)^2-4(x-1)(x+1) = 49`

`⇔ 4x^2+12x+9-4(x^2-1) = 49`

`⇔ 4x^2+12x+9-4x^2+4 = 49`

`⇔ 12x+13 = 49`

`⇔ 12x = 36`

`⇔ x = 3`

`\text{Vậy S=}` `{3}`

`c)`

`(2x+1)(1-2x)+(1-2x)^2 = 18`

`⇔ (1+2x)(1-2x)+1-4x+4x^2 = 18`

`⇔ 1-4x^2+1-4x+4x^2 = 18`

`⇔ -4x+2 = 18`

`⇔ -4x = 16`

`⇔ x = -4`

`\text{Vậy S=}` `{-4}`

`d)`

`(3x-1)^2-(3x-2)^2 = 0`

`⇔ (3x-1-3x+2)(3x-1+3x-2) = 0`

`⇔ 6x-3 = 0`

`⇔ 6x = 3`

`⇔ x = 1/2`

`\text{Vậy S=}` `{1/2}`

Vote (0) Phản hồi (0) 2 năm trước

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