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Answer 1 · 2017-11-06T02:39:40

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Let #a=x+5# and #b=x-5#

Then, the equation reads #a^2-b^2#.

#a^2-b^2=(a+b)*(a-b)#

#=((x+5)+(x-5))*((x+5)-(x-5))#

#=(2x)(10)#

#=20x#

#=4*(5x)#

Since we know #5x# is an integer (contained in #ZZ#), then the original expression is divisible by #4#.