Giải thích các bước giải:
Từ đề suy ra:
$A=\dfrac{1-3^2}{3^2}\cdot \dfrac{1-4^2}{4^2}\cdots\dfrac{1-50^2}{50^2}$
$\to A=\dfrac{3^2-1}{3^2}\cdot \dfrac{4^2-1}{4^2}\cdots\dfrac{50^2-1}{50^2}$
$\to A=\dfrac{(3-1)(3+1)}{3^2}\cdot \dfrac{(4-1)(4+1)}{4^2}\cdots\dfrac{(50-1)(50+1)}{50^2}$
$\to A=\dfrac{2.4}{3^2}\cdot \dfrac{3.5}{4^2}\cdots\dfrac{49.51}{50^2}$
$\to A=\dfrac{2.3....49}{3.4....50}\cdot \dfrac{4.5....51}{3.4...50}$
$\to A=\dfrac{2}{50}\cdot \dfrac{51}{3}$
$\to A=\dfrac{17}{25}$
