Tính: a) (x + 2y)^2; b) (x – 3y)(x + 3y); c) (5 – x)^2 .
Tính:
a) (x + 2y)2;
b) (x – 3y)(x + 3y);
c) (5 – x)2 .
a) (x + 2y)2
= x2 + 2 . x . 2y + (2y)2
= x2 + 4xy + 4y2
b) (x – 3y)(x + 3y) = x2 – (3y)2 = x2 – 9y2
c) (5 – x)2 = 52 – 2 . 5 . x + x2 = 25 – 10x + x2.