1.

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

Answer»

f(x) = 4x – x2

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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