$a$)Ta có :
$\dfrac{2525}{5353} = \dfrac{25:101}{53:101} = \dfrac{25}{53}$
$\dfrac{252525}{535353} = \dfrac{25:10101}{53:10101} = \dfrac{25}{53}$
$⇒ \dfrac{25}{53} = \dfrac{2525}{5353} = \dfrac{252525}{535353}$ ($đpcm$)
$b$)Ta có :
$\dfrac{3737}{4141} = \dfrac{37:101}{41:101} = \dfrac{37}{41}$
$\dfrac{373737}{414141} = \dfrac{37:10101}{41:10101} = \dfrac{37}{41}$
$⇒ \dfrac{37}{41} = \dfrac{3737}{4141} = \dfrac{373737}{414141}$ ($đpcm$)