Bài 1:
a)Ta có: $5^{28}$=$25^{14}$
Vì 25<26 nên $25^{14}$<$26^{14}$⇒$5^{28}$<$26^{14}$
b)Ta có: $5^{30}$=$125^{10}$
Vì 125>124 nên $125^{10}$>$124^{10}$⇒$5^{30}$<$124^{10}$
c)Ta có: $34^{11}$=$2^{11}$.$17^{11}$
$17^{14}$=$17^{11}$.$17^{3}$
Vì $2^{11}$<$17^{3}$ (2048<4913) nên $2^{11}$.$17^{11}$<$17^{11}$.$17^{3}$
⇒$34^{11}$<$17^{14}$
d)Ta có: $4^{21}$=$4^{2.7}$=$64^{7}$
⇒$4^{21}$=$64^{7}$
Bài 2:
a)$5^{n}$=625
$5^{n}$=$5^{4}$
⇒n=4 (thỏa mãn)
Vậy n=4
b)n²=169
⇒n=√169 hoặc n=-√169
n=13 (thỏa mãn) hoặc n=-13 (không thỏa mãn)
Vậy n=13