1.

If f(x) = x2 + 3x then show that ∆f(x) = 2x + 4

Answer»

f(x) = x2 + 3 x 

∆f(x) = f(x + h) – f(x) 

= (x + h)2 + 3(x + h) – x2 – 3x 

= x2 + 2xh + h2 + 3x + 3h – x2 – 3x 

= 2xh + 3h + h2  

Put h = 1, ∆f(x) = 2x + 4



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