Answer
$(x-5-6y)(x-5+6y)$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $x^2-10x+25-36y^2=\\=x^2-2\cdot x\cdot5+5^2-(6y)^2\\=(x-5)^2-(6y)^2\\=(x-5-6y)(x-5+6y)$