Toán Lớp 8: Tính:
a) (x + 2y)2
b) (x – 3y)(x + 3y)
c) (5 – x)2
d) (x – 1)3
e) (3 – y)2
f) (2x + 3y)3
g) (5x – y)2
h) (x + 4)( x2 – 4x + 16)
i) (x – 3y)(x2 + 3xy + 9y2)
j) (y – 3)(y + 3)
k) (m + n)(m2 – mn + n2)
l) (2 – a)(4 + 2a + a2)
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A/(x+2y)2
=2.x+2.2y
=2x+4y
B/(x-3y)(x+3y)
=x.x+x.3y-3y.x-3y.3y
=x mũ 2+3xy-3xy-9y mũ 2
=x mũ 2-9y mũ 2
C/(5-x)2
=2.5-x.2
=10-2x
D/(x-1)3
=3.x-1.3
=3x-3
E/(3-y)2
=2.3-y.2
=6-2y
F/(2x+3y)3
=3.2x+3.3y
=6+9y
G/(5x-y)2
=2.5x-y.2
=10x-2y
H/(x+4)(x2-4x+16)
=2x.x-4x.x+16.x+2x.4-4x.4+16.4
=2x mũ 2-4x mũ 2+16x+8x-16x+64
=(2x mũ 2-4x mũ 2)+(16x+8x-16x)+64
=-2x mũ 2 +8x+64
K/(m+n)(2m-mn+2n)
=m.2m+m.(-mn)+m.2n+n.2m+n.(-mn)+n.2n
=2m mũ 2-m mũ 2n+2mn+2mn-m n mũ 2+2 N mũ 2