Toán Lớp 8: Tìm x 1.16x ² -(4x-5) ²=15 2.(2x+1)(1-2x)+(1-2x) ²=18 3.(x-5) ²-(x+4)=9 4.(2x+3) ² -4(x-1)(x+1)=49 giúp mình ạ

Question

Toán Lớp 8:  Tìm x 1.16x ² -(4x-5) ²=15 2.(2x+1)(1-2x)+(1-2x) ²=18 3.(x-5) ²-(x+4)=9 4.(2x+3) ² -4(x-1)(x+1)=49 giúp mình ạ

maingocquynhnhu2k1 · Answer

Giải đáp:

Lời giải và giải thích chi tiết:

a)\(16x^2-\left(4x-5\right)^2=15\)

\(\Rightarrow\left(4x\right)^2-\left(4x-5\right)^2-15=0\)

\(\Rightarrow\left(4x-4x+5\right)\left(4x+4x-5\right)-15=0\)

\(\Rightarrow5\left(8x-5\right)-15=0\)

\(\Rightarrow40x-25-15=0\)

\(\Rightarrow40x-40=0\)

\(\Rightarrow x=1\)

– – – – –

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

<=> (1-2x)(2x+1+1-2x)=18

<=>2(1-2x)=18

<=>2-4x=18

<=>-16=4x

<=>x=-4

– – – – –

(x-5)^2-(x+4)=9

(x-5)(x-5)-(x+4)=9

x(x-5)-5(x-5)-(x+4)=9

x^2-5x-5(x-5)-(-+4)=9

x^2-5x-5x+25-(x+4)=9

x^2-10x+25 – (x+4)=9

x = (11 +- \sqrt{73})/2

– – – – –

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

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

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

4x^2+6x+3(2x+3)-4(x-1)(x+1)=49

4x^2+6x+6x+9-4(x-1)(x+1)=49

4x^2+12x+9-4(x-1)(x+1)=49

x = 3

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