Đáp án:
Giải thích các bước giải:
Bài 4:
$B=\dfrac{3^{13}.13+3^{13}.3}{3^{13}.2^4}=\dfrac{3^{13}.(13+3)}{3^{13}.16}=\dfrac{3^{13}.16}{3^{13}.16}=1$
Bài 7:
$a,7^6+7^5-7^4$
$=7^4(7^2+7-1)$
$=7^4.(49+7-1)$
$=7^4.55$
$\text{Vì $55\vdots11$ nên $7^4.55\vdots11$}$
$\text{=>đpcm}$
$b,27^8-3^{21}$
$=3^{24}-3^{21}$
$=3^{21}(3^3-1)$
$=3^{21}.26$
$\text{Vì $26\vdots26$ nên $3^{21}.26\vdots26$}$
$\text{=>đpcm}$
$c,8^{12}-2^{33}-2^{30}$
$=2^{36}-2^{33}-2^{30}$
$=2^{30}(2^6-2^3-1)$
$=2^{30}.(64-8-1)$
$=2^{30}.55$
$\text{Vì $55\vdots55$ nên $2^{30}.55\vdots55$}$
$\text{=>đpcm}$
