Question

Use an appropriate identity to find 105 multipled by 98.

Answer 1

Dear Student,

$$\begin{gathered} 105\times 98 \\ =\left(100+5\right)\times \left(100-2\right) \\ ={100}^2+\left(5-2\right)\times 100+5\times \left(-2\right)\left(\mathrm{Using}\mathrm{identity}\left(\mathrm{x}+\mathrm{a}\right)\left(\mathrm{x}+\mathrm{b}\right)={\mathrm{x}}^2+\left(\mathrm{a}+\mathrm{b}\right)\mathrm{x}+\mathrm{ab}\right) \\ =10000+300-10 \\ =10290\mathrm{ANS}... \end{gathered}$$

Regards