BigDecimal strings are a new and powerful tool. The new math routines in Basic 5.7 are all approximations. Sin, Cos, Tan all return the closest approximation of an irrational number, rounded by the specified maxDigits. It's very important to be aware of the rounding. For instance, if you want to get the cosine of Pi feed the cos function Pi calculated to a few extra decimal places than you require from the cos function.
Print BigCos$(BigPi$(25), 20)
Basic 5.7 will be released as soon as the documentation is complete.