36а^2-49= (6а-7)(6а+7)

-81+25у^2= 25у^2-81= (5у-9)(5у+9)

47^2-37^2= (47-37)(47+37)= 10×84=840

b^2-4/9= (b-2/3)(b+2/3)

64-25x^2= (8-5х)(8+5х)

-49а^2+16b^2= 16b^2-49a^2= (4b-7a)(4b+7a)

53^2-63^2= (53-63)(53+63)= -10×116= -1160

25/49-p^2= (5/7-p)(5/7+p)