a) =21.7² -11.7²  +90.7² + 7².125.16

=7².(21-11+90+125.16)

=7² .2100

=102900

b)

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

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

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

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

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

+) \(a\times a^5:a^2=a^{1+5-2}=a^4\)

+) \(a^5\times a^2:a^6=a^{5+2-6}=a\)

_Chúc bạn học tốt_

a.a^5:a^2=a^6:a^2=a^4

a^5.a^2:a^6=a^7:a^6=a

giỏi đăng hey

giỏi quá chứ hì

\(\frac{x+1}{2}=\frac{8}{x+1}\)

\(\Rightarrow\left(x+1\right)^2=16\)

\(\Rightarrow\orbr{\begin{cases}x+1=4\\x+1=-4\end{cases}}\Rightarrow\orbr{\begin{cases}x=3\\x=-5\end{cases}}\)

\(\frac{x+1}{2}=\frac{8}{x+1}\Rightarrow\left(x+1\right).\left(x+1\right)=2.8\)

\(\Rightarrow2\left(x+1\right)=16\Rightarrow x+1=8\Rightarrow x=7\)

5^2x—3–2.5²=5².3( đề vầy phải ko bạn)

5^2x—3–2.25=25.3

5^2x—3–2.25=75

5^2x—3–2=75:25

5^2x—3–2=3

5^2x—3=3+2

5^2x—3=5¹

==> 2x—3=1

==> 2x=1+3

==> 2x=4

x=4:2

x=2

|2x—7| =20+5.(—3)

|2x—7| = 20+(—15)

|2x—7| = 5

==> 2x—7=—5 hoặc 2x—7=5

==> 2x=—5+7 hoặc 2x= 5+7

==> 2x= 2 hoặc 2x=12

==> x=2:2 hoặc x=12:2

==> x=1 hoặc x=6

\(Ư_{\left(a\right)}=\left\{\mp1;\mp5;\mp13;\mp65\right\}\)

\(Ư_{\left(b\right)}=\left\{\mp1;\mp2;\mp4;\mp8;\mp16;\mp32\right\}\)

\(Ư_{\left(c\right)}=\left\{\mp1;\mp3;\mp7;\mp9;\mp21;\mp63\right\}\)

HOK TỐT .

a = 5 . 13 có các ước là 1, 5, 13, 65

b = 2⁵ có các ước là 1, 2, 2², 2³, 2⁴, 2⁵ hay 1, 2, 4, 8, 16, 32

c = 3² . 7 có các ước là 1, 3, 3², 7, 3 . 7, 3² . 7 hay 1, 3, 9, 7, 21, 63