Maths!!!

1.
9a^2 - k^2 + 2kc -c^2
=9a² - k² + 2kc -c²
=9a² -(k² - 2kc +c²)
=(3a)² -(k-c)².............................a²-2ab+b²=(a-b)²
=(3a+k-c)(3a-k+c)......................a²-b²=(a-b)(a+b)

2.
4x^2 - 20x +25 - y^2
=4x² - 20x +25 - y²
=(2x)²-2(2x)(5)+(5)² -y²
=(2x-5)² -y².................................a²-2ab+b²=(a-b)²
=(2x-5-y)(2x-5+y)........................a²-b²=(a-b)(a+b)