ક્ષેત્રફળ \( A = ℓ × b = 5.7 ×3.4 = 19.38 cm^2\)

\(\frac{{\Delta A}}{A}\,\, = \,\, \pm \,\,\left( {\frac{{\Delta \ell }}{\ell }\,\, + \,\,\frac{{\Delta b}}{b}} \right)\,\,\, = \,\, \pm \,\,\left( {\frac{{0.1}}{{5.7}}\,\, + \;\,\frac{{0.2}}{{3.4}}} \right)\,\, = \,\, \pm \,\,\left( {\frac{{0.34\,\, + \,\,1.14}}{{5.7\,\, \times \,\,3.4}}} \right)\, = \,\, \pm \,\,\frac{{1.48}}{{19.38}}\)

\(\Delta A\,\, = \,\, \pm \,\,\frac{{1.48}}{{19.38}}\,\, \times \,\,A\,\, = \,\, \pm \,\,\frac{{1.48}}{{19.38}}\,\, \times \,\,19.8\,\, = \,\, \pm 1.48\,\,\)

ક્ષેત્રફળ \( = \,\,\left( {19.38\,\, \pm \,\,1.48} \right)\,\,sq.cm\)