(2x+5)square -(2x-5)square
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(2x+5)^2-(2x-5)^2=(2x+5+2x-5)(2x+5-2x+5)
=4x(10)=40x
using identity
=>(a+b)²=a²+b²+2ab
=>(a-b)²=a²+b²-2ab
4x²+25+20x-(4x²+25-20x)
=4x²+25+20x-4x²-25+20x
=20x+20x
=40x
x=-40