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

Toán Lớp 8: 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

Tháng Mười Hai 6, 2022 Toán học 2 Comments 0 views

Toán Lớp 8: 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

Comments ( 2 )

  1. behocgioitoan
    behocgioitoan
    6 Tháng Mười Hai, 2022 at 4:04 sáng
    Reply
    16x^2-(4x-5)^2=15
    ⇔ 16x^2 – 16x^2 + 40x – 25 = 15
    ⇔ 40x = 15 + 25
    ⇔ 40x = 40
    ⇔ x = 1
    Vậy S = {1}
    _________________________________
    (2x+3)^2-4(x-1)(x+1)=49
    ⇔ 4x^2 + 12x + 9 – 4x^2 + 4 = 49
    ⇔ (4x^2-4x^2) + 12x = 49 – 4 – 9
    ⇔ 12x = 36
    ⇔ x = 3
    Vậy S = {3}
    _________________________________________
    (2x+1)(1-2x)+(1-2x)^2=18
    ⇔ 1 – 4x^2 + 1 – 4x + 4x^2 = 18
    ⇔ (4x^2-4x^2) – 4x = 18 – 1 – 1
    ⇔ -4x = 16
    ⇔ x = -4
    Vậy S = {-4}
    __________________________________
    (3x-1)^2-(3x-2)^2=0
    ⇔ 9x^2 – 6x + 1 – 9x^2 + 12x – 4 = 0
    ⇔ (9x^2-9x^2) + 6x = 0 + 4 – 1
    ⇔ 6x = 3
    ⇔ x = 1/2
    Vậy S = {1/2}

  2. thanhthuythu
    thanhthuythu
    6 Tháng Mười Hai, 2022 at 4:04 sáng
    Reply
    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
     

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

Nguyệt Minh

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