Question

Using suitable identity evaluate the following : 98^3

Answer 1

941,192

Steps:

$(a-b)^3=a^3-b^3-3a^2b+3ab$

$\begin{gathered} (98)^3=(100-2)^3 \\ (100-2)^{3\text{ }}=(100)^3-(2)^3-3\cdot(100)^2\cdot2+3\cdot100\cdot2^2\text{ } \\ (100)^3-(2)^3-3\cdot(100)^2\cdot2+3\cdot100\cdot2^2\text{ = 1,0}00,000\text{ - 3 - 60,000 +1,200} \\ \text{ 1,0}00,000\text{ - 3 - 60,000 +1,200 = 941,192} \end{gathered}$