helping granddaughter with math homework

[Lissa]

Next time just remember that sin(x) is about x for small values of x, and cos(x) is about 1 - x^2/2 for small values of x. Or memorize the Taylor expansions, they're not very complicated for sin and cos.

Problem is, you typically never use small radian values, you normally are using radian values of x*pi/2 and x*pi/3 where x is typically 1/4, 1/2, 3/4, 1, 2, 3, and 4.