Question

làm giùm em bài 10 với 11 đc hong ạ.em cần gấp lắm. :'(

Answer 1

10.

a, \(2n+1;2n+3;2n+5\left(n\in N\right)\)

b, Gọi ba số cần tìm là \(2n+1;2n+3;2n+5\left(n\in N\right)\)

Ta có:

\(\left(2n+1\right)\left(2n+3\right)+20=\left(2n+3\right)\left(2n+5\right)\\ 4n^2+2n+6n+3+20=4n^2+10n+6n+15\\ 4n^2-4n^2+2n-10n+6n-6n=15-3-20\\ -8n=-8\\ n=1\\ \Rightarrow\left\{{}\begin{matrix}2n+1=2\cdot1+1=3\\2n+3=2\cdot1+3=5\\2n+5=2\cdot1+5=7\end{matrix}\right.\)

Vậy 3 số cần tìm là 3; 5; 7

11.

\(x=79\Rightarrow80=x+1\\ P\left(x\right)=x^7-\left(x+1\right)x^6+\left(x+1\right)x^5-\left(x+1\right)x^4+...+\left(x+1\right)x+15\\ =x^7-x^7-x^6+x^6+x^5-x^5-x^4+...+x^2+x+15\\ =x+15\\ P\left(79\right)=79+15=94\)

Vậy ...