Toán Lớp 8: 4x^2-25-(2x-5) nhân 2x+7 =0 tìm x
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Toán Lớp 8: 4x^2-25-(2x-5) nhân 2x+7 =0 tìm x
Comments ( 2 )
<=> (4x^2 – 25) – (2x – 5)(2x + 7) = 0
<=> (2x – 5)(2x + 5) – (2x – 5)(2x + 7) = 0
<=> (2x – 5)[(2x + 5) – (2x + 7)] = 0
<=> (2x – 5)(2x + 5 – 2x – 7) = 0
<=> (2x – 5). (-2) = 0
<=> 2x – 5 = 0
<=> 2x = 5
<=> x = 5/2
Vậy . . .
$\text{$4x^{2}$ – 25 ( 2x .- 5 ) . ( 2x + 7 ) = 0 }$
$\text{= 4x² – 25 – ( 4x² + 14x – 10x – 35 ) = 0 }$
$\text{= – 4x² – 4x² – 4x – 25 + 35 = 0 }$
$\text{= 0 – 4x + 10 = 0 }$
$\text{= 4x = 10 }$
$\text{= $\frac{10}{4}$ = $\frac{5}{2}$ }$
$\text{suy ra x = $\frac{5}{2}$ }$