f(x)= 1+2x , x0=4 , del`ta x =0.001
del'ta y=f(x0+del'ta x)-f(x0)=1+2(x0+del'ta x)-(x0+del,ta x)= 1+2(4+0.01)-(4*2+0.01)=9.02-9=0.02