If f(x) = 4x – x2, x R, then write the value of f(a + 1) – f(a – 1).


f(a+1)-f(a-1) =[4(a+1) -(a+1)2]-[4(a-1)-(a-1)2 ]


=4[(a+1) -(a-1)]- [ (a+1)2 -(a+1)2]


=4(2)-[(a+1+a-1) (a+1-a+1)]


Using: a2 -b2= (a + b)(a-b)


f(a+1)-f(a-1)=4(2)-2a(2)


=4(2-a)


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