Is there any wrong with this BigDecimal calculation?

Question

I am new to BigDecimal.
I tried some math calculations using Java code. When I try the same calculations using Google calculator it gives me a slightly different results. Which one is the most accurate?. If Google calculator is more accurate, then how to improve java code to match it?.

On Google calculator:

134.23576185216913 - (134.23576185216913 × √(1 - (200000000^2 ÷ 299800000^2))) = 34.2357618522

On Java:

      BigDecimal t1 = new BigDecimal(134.23576185216913);
      BigDecimal one = new BigDecimal(1);
      BigDecimal speed = new BigDecimal(200000000).pow(2);
      BigDecimal lightsSpeed = new BigDecimal(299800000).pow(2);

      MathContext mc = new MathContext(2, RoundingMode.HALF_UP);
      System.out.println(t1.subtract((t1.multiply(SquareRoot.bigSqrt(one.subtract(speed.divide(lightsSpeed,mc)))))));

The method of bigSqrt is from here

The result is:

run: 34.683856455950090090043113321827989040137639817587194953722595479211000578082422197809603912048352550091209304856567024386365147605287692511973841869226169664820176852861655846233912503305984796190828666994508412096618025960010635831985100961879858807909056676663493607611105279976694118991120829708264297254294821755138400476425886154174804687500
BUILD SUCCESSFUL (total time: 0 seconds)

Answer 1

This is your issue:

MathContext mc = new MathContext(2, RoundingMode.HALF_UP);

your are rounding the division to 2 decimal places. Use MathContext mc = new MathContext(15, RoundingMode.HALF_UP); instead (for example) and you should get something closer to the expected result.

You can see the difference with:

System.out.println(speed.divide(lightsSpeed,new MathContext(2, RoundingMode.HALF_UP)));
System.out.println(speed.divide(lightsSpeed,new MathContext(15, RoundingMode.HALF_UP)));

which prints:

0.45
0.445037630156818