Toán Câu 1 : a ) x ³ – x b ) 2x ² – 3x – 9 = 0 06/12/2021 By Eva Câu 1 : a ) x ³ – x b ) 2x ² – 3x – 9 = 0
a ) x³ – x = x ( x² – 1 ) = x ( x – 1 ) ( x + 1 ) b ) 2x² – 3x – 9 = 0 ⇔ x² – 3x + x² – 9 = 0 ⇔ x ( x – 3 ) + ( x – 3 ) ( x + 3 ) = 0 ⇔ ( x – 3 ) ( x + x + 3 ) =0 ⇔ ( x – 3 ) ( 2x + 3 ) = 0 ⇔ x – 3 = 0 2x + 3 = 0 ⇔ x = 3 x = 1.5 Trả lời
a ) x³ – x
= x ( x² – 1 )
= x ( x – 1 ) ( x + 1 )
b ) 2x² – 3x – 9 = 0
⇔ x² – 3x + x² – 9 = 0
⇔ x ( x – 3 ) + ( x – 3 ) ( x + 3 ) = 0
⇔ ( x – 3 ) ( x + x + 3 ) =0
⇔ ( x – 3 ) ( 2x + 3 ) = 0
⇔ x – 3 = 0
2x + 3 = 0
⇔ x = 3
x = 1.5
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