Answer:
(x+25)(x-21)
Step-by-step explanation:
x²+4x-525
=x²-21x+25x-525
=x(x-21)+25(x-21)
=(x+25)(x-21)
multiply to get -525
add to get 4
(x²+21x)(+25x-525)
factorise:
x²+21x
x(x-21)
25x-525
25(x-21)
