Câu 1 :
a ) 3x ( x – 5 )
b ) ( 7x – 1 ) ( 7x + 1 )
c ) x ² + 6x + 9 – y ²
Câu 1 : a ) 3x ( x – 5 ) b ) ( 7x – 1 ) ( 7x + 1 ) c ) x ² + 6x + 9 – y ²
By Athena
By Athena
Câu 1 :
a ) 3x ( x – 5 )
b ) ( 7x – 1 ) ( 7x + 1 )
c ) x ² + 6x + 9 – y ²
Đáp án:
`a) 3x(x-5)=3x^2-15x`
`b) (7x-1)(7x+1)=(7x)^2-1^2=49x^2-1`
`c) x^2+6x+9-y^2=(x^2+6x+9)-y^2=(x+3)^2-y^2=(x+3-y)(x+3+y)`
Câu 1 :
a ) 3x ( x – 5 )
b ) ( 7x – 1 ) ( 7x + 1 )
c ) x ² + 6x + 9 – y ²
TL :
a ) 3x ( x – 5 )
= 3x² – 15x
b ) ( 7x – 1 ) ( 7x + 1 )
= ( 7x )² – 1²
c ) x ² + 6x + 9 – y ²
= ( x² + 6x + 9 ) – y²
= ( x + 3 ) ² – y²
= ( x + 3 – y ) ( x + 3 + y )