A useful approximation is a close estimate or guess that helps us understand or solve something, even if it's not 100% accurate. It's a helpful and practical way to get an idea or answer without needing complete precision. Full definition
Equations like the above let you approach the problem analytically, in that I can calculate useful approximations like the derivative of mortgage length with respect to downpayment, or interest rates, or payment amount, or payment frequency, in a continuous manner. (money.stackexchange.com)
There are useful approximations where the interference terms can be neglected. (scientificamerican.com)
The Ackermann steering mechanism is a very useful approximation but it is an approximation and is only correct straight ahead and at one steer angle. (greencarcongress.com)