How do you find the linear approximation of (1.999)^4(1.999)4 ?

1 Answer
Aug 17, 2014

You can use the tangent line approximation to create a linear function that gives a really close answer.

Let's put f(x) = x^4,f(x)=x4, we want f(1.999)f(1.999) so use x= 1.999 and the nearby point of tangency a = 2. We'll need f'(x)=4x^3 too.

The linear approximation we want (see my other answer) is

f(x) ~~ f(a) + f'(a)(x-a)

f(1.999) ~~ f(2) + f'(2)(1.999-2)

~~ 2^4 + 4*2^3*(-0.001) = 16 - 0.032 = 15.968

You can compare to the actual exact result of
1.999^4 = 15.968023992001, so we came pretty close!

Bonus insight: The error depends on higher derivatives and can be predicted in advance! \ dansmath strikes again, approximately! /