Toán Lớp 8: Khai triển các hằng đẳng thức sau:
a) (5/3x + 2/3y)^3
b) (4/3x + 3/2y^2)^3
c) (3/2y^2 +1/3)^2
d) 1/9x^2 – 9/4y^2
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Toán Lớp 8: Khai triển các hằng đẳng thức sau:
a) (5/3x + 2/3y)^3
b) (4/3x + 3/2y^2)^3
c) (3/2y^2 +1/3)^2
d) 1/9x^2 – 9/4y^2
Comments ( 2 )
c)9/4y^4+y^2+1/9
d)(1/3x+3/2y)(1/3x-3/2y)
=(5/3x)^3+3. (5/3x)^2 . 2/3y+3. 5/3x .(2/3y)^2+(2/3y)^3
=125/27x^3+50/9x^2y+20/9xy^2+8/27y^3
Áp dụng HĐT:(A+B)^3=A^3+3A^2B+3AB^2+B^3
=(4/3x)^3+3. (4/3x)^2 . 3/2y^2+3. 4/3x .(3/2y^2)^2+(3/2y^2)^3
=64/27x^3+8x^2y^2+9xy^4+27/8y^6
Áp dụng HĐT:(A+B)^3=A^3+3A^2B+3AB^2+B^3
=(3/2y^2)^2+2. 3/2y^2 . 1/3+(1/3)^2
=9/4y^4+y^2+1/9
Áp dụng HĐT:(A+B)^2=A^2+2AB+B^2
=(1/3x)^2-(3/2y)^2
=(1/3x+3/2y)(1/3x-3/2y)
Áp dụng HĐT:A^2-B^2=(A+B)(A-B)