B

3km 12m =......................m

A. 312

B. 3012

C. 36

D. 15

B

SAO K CÓ ĐỀ BÀI VẬY BẠN

36: 32=34

Vậy chọn đap án E

Đáp án là B

a: \(24\cdot16=2^3\cdot3\cdot2^4=2^7\cdot3\)

c: \(75:\left(7\cdot72\right)=\dfrac{3\cdot5^2}{7\cdot3^2\cdot2^2}=\dfrac{5^2}{7\cdot3\cdot2^2}\)

3012

3012

3012

a) 199¹⁵ . 199²⁵ = 199^{15 + 25} = 199⁴⁰

b) 35²⁰¹⁹ : 35²⁰¹² = 35^{2019 - 2012} = 35⁷

c) a . a⁹⁹ = a^{1 + 99} = a¹⁰⁰

d) x : x¹⁵ . x⁶ = x^{1 - 15} . x⁶ = x^-14 . x⁶ = x^{-14 + 6} = x^-8

e) 16 . 2⁵ = (2⁴)¹ . 2⁵ = 2⁴ . 2⁵ = 2^{4 + 5} = 2⁹

g) 49 . 7⁵ = 7² . 7⁵ = 7^{2 + 5} = 7⁷

h) 36 . 2¹⁶ = (bí r!)

k) a²⁰¹⁹ : a²⁰¹⁵ = a^{2019 - 2015} = a⁴

Ta có : \(a^2+b^2=c^2+d^2\)

\(\Leftrightarrow a^2-c^2=d^2-b^2\)

\(\Leftrightarrow\left(a-c\right)\left(a+c\right)=\left(d-b\right)\left(d+b\right)\)

Do \(a+b=c+d\Rightarrow a-c=d-b\)

\(\Rightarrow\left(a-c\right)\left(a+c\right)=\left(a-c\right)\left(d+b\right)\)

\(\Leftrightarrow\left(a-c\right)\left(a+c-b-d\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}a-c=0=d-b\\a+c=b+d\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}a=c\\d=b\end{matrix}\right.\\a+c=b+d\end{matrix}\right.\)

Với a = c ; d = b \(\Rightarrow a^{2012}+b^{2012}=c^{2012}+d^{2012}\left(đpcm\right)\)

Với \(a+c=b+d\)

Mà \(a+b=c+d\)

\(\Rightarrow a+c+a+b=b+d+c+d\)

\(\Rightarrow2a=2d\Rightarrow a=d\Rightarrow a^{2012}=d^{2012}\left(1\right)\)

Lại có : \(a+c=b+d\)

\(\Rightarrow b=c\Rightarrow b^{2012}=c^{2012}\left(2\right)\)

Từ ( 1 ) ; ( 2 )

\(\Rightarrow a^{2012}+b^{2012}=c^{2012}+d^{2012}\left(đpcm\right)\)