Use the Binomial Theorem to write the first three terms of the binomial. \[ (a+b)^{20} \]

Step 1 ：Using the Binomial Theorem, we can write the first three terms of the binomial \((a+b)^{20}\) as follows:

Step 2 ：The first term is \(\binom{20}{0}a^{20}b^{0}=a^{20}\).

Step 3 ：The second term is \(\binom{20}{1}a^{19}b^{1}=20a^{19}b\).

Step 4 ：The third term is \(\binom{20}{2}a^{18}b^{2}=190a^{18}b^{2}\).

Step 5 ：So, the first three terms of the binomial \((a+b)^{20}\) are \(\boxed{a^{20}+20a^{19}b+190a^{18}b^{2}}\).