Question

Tính hợp lí 

a)\(21.7^2-11.7^2+90.7^2+49.125.16\)

b)\(\frac{5.4^{15}.9^9-4.3^{20}.8^9}{5.2^9.6^{19}-7.2^{29}.27^6}\)

Answer 1

a) =21.7² -11.7²  +90.7² + 7².125.16

=7².(21-11+90+125.16)

=7² .2100

=102900

b)

=\(\frac{5.2^{30}.3^{18}-2^2.3^{20}.2^{27}}{5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}}\)

=\(\frac{5.2^{30}.3^{18}-2^{29}.3^{20}}{5.2^{28}.3^{19}-7.2^{29}.3^{18}}\)

=\(\frac{2^{29}.3^{18}.\left(5.2-3^2\right)}{2^{28}.3^{18}.\left(5.3-7.2\right)}\)

=\(\frac{2\left(5.2-3^2\right)}{5.3-7.2}\)

=\(\frac{2\left(10-9\right)}{15-14}=\frac{2.1}{1}=2\)