(2с-7d)(2c+7d)
(xy-0.2)(xy+0.2)
(ab-c)(ab+c)
(pq-2k)(pq+2k)
1)4c^2-49d^2=(2c-7d)(2c+7d)
2)x^2y^2-0,04=(xy-0.2)(xy+0.2)
3)a^2b^2-c^2=(ab-c)(ab+c)
4)p^2q^2-4k^2=(pq-2k)(pq+2k)
a^2-b^2=(a-b)(a+b)
