Answer :
[tex]20x^2-45=5(4x^2-9)=5[(2x)^2-3^2]=5(2x-3)(2x+3)\\\\--------------------------\\\\use:a^2-b^2=(a-b)(a+b)[/tex]
[tex](a+b)(a-b)=a^2-b^2\\---------------------\\\\20x^2-45=5\cdot4x^2-5\cdot9=5\cdot(4x^2-9)=\\\\.\ \ \ \ \ \ \ \ \ \ \ \ =5\cdot[(2x)^2-3^2]=5\cdot(2x+3)(2x-3)[/tex]
